feat: inline review comments on specific lines

Findings that reference a file+line within the diff are now posted as
inline comments directly on that line, in addition to appearing in the
summary table. Findings outside the diff range stay in the body only.

Implementation:
- gitea/diff.go: ParseDiffNewLines extracts new-file line numbers from
  each hunk in the unified diff
- gitea/client.go: PostReview accepts optional []ReviewComment with
  path + new_position + body (omitempty when nil)
- cmd/review-bot/main.go: maps findings → inline comments when the line
  exists in the diff, passes them to PostReview

Tests:
- diff parser: multi-hunk, new files, empty diff, boundary lines
- PostReview: with comments, nil comments (omitted from payload)

gitea/client.go

@@ -57,6 +57,13 @@ type ChangedFile struct {
 	Status   string `json:"status"`
 }
 
+// ReviewComment represents an inline comment to attach to a review.
+type ReviewComment struct {
+	Path        string `json:"path"`
+	NewPosition int64  `json:"new_position"`
+	Body        string `json:"body"`
+}
+
 // GetPullRequest fetches PR metadata.
 func (c *Client) GetPullRequest(ctx context.Context, owner, repo string, number int) (*PullRequest, error) {
 	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d", c.baseURL, owner, repo, number)
@@ -131,15 +138,18 @@ func (c *Client) GetFileContentRef(ctx context.Context, owner, repo, filepath, r
 
 // PostReview submits a review to a PR and returns the created review.
 // event should be "APPROVED" or "REQUEST_CHANGES".
-func (c *Client) PostReview(ctx context.Context, owner, repo string, number int, event, body string) (*Review, error) {
+// comments are optional inline comments attached to specific lines.
+func (c *Client) PostReview(ctx context.Context, owner, repo string, number int, event, body string, comments []ReviewComment) (*Review, error) {
 	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d/reviews", c.baseURL, owner, repo, number)
 
 	payload := struct {
-		Body  string `json:"body"`
-		Event string `json:"event"`
+		Body     string          `json:"body"`
+		Event    string          `json:"event"`
+		Comments []ReviewComment `json:"comments,omitempty"`
 	}{
-		Body:  body,
-		Event: event,
+		Body:     body,
+		Event:    event,
+		Comments: comments,
 	}
 
 	data, err := json.Marshal(payload)

gitea/client_test.go

@@ -128,7 +128,7 @@ func TestPostReview(t *testing.T) {
 	defer server.Close()
 
 	client := NewClient(server.URL, "test-token")
-	review, err := client.PostReview(context.Background(), "owner", "repo", 3, "APPROVED", "LGTM")
+	review, err := client.PostReview(context.Background(), "owner", "repo", 3, "APPROVED", "LGTM", nil)
 	if err != nil {
 		t.Fatalf("unexpected error: %v", err)
 	}
@@ -175,7 +175,7 @@ func TestPostReview_Non200(t *testing.T) {
 	defer server.Close()
 
 	client := NewClient(server.URL, "test-token")
-	_, err := client.PostReview(context.Background(), "owner", "repo", 1, "APPROVED", "test")
+	_, err := client.PostReview(context.Background(), "owner", "repo", 1, "APPROVED", "test", nil)
 	if err == nil {
 		t.Fatal("expected error for 403, got nil")
 	}

gitea/diff.go

@@ -0,0 +1,76 @@
+package gitea
+
+import (
+	"strconv"
+	"strings"
+)
+
+// DiffLineRanges maps filenames to the set of new-file line numbers present in the diff.
+type DiffLineRanges struct {
+	files map[string]map[int]bool
+}
+
+// Contains reports whether the given file+line is within the diff hunks.
+func (d *DiffLineRanges) Contains(file string, line int) bool {
+	if d == nil || d.files == nil {
+		return false
+	}
+	lines, ok := d.files[file]
+	if !ok {
+		return false
+	}
+	return lines[line]
+}
+
+// ParseDiffNewLines parses a unified diff and extracts the new-file line numbers
+// that appear in each hunk (both added and context lines).
+func ParseDiffNewLines(diff string) *DiffLineRanges {
+	result := &DiffLineRanges{files: make(map[string]map[int]bool)}
+
+	var currentFile string
+	var newLine int
+
+	for _, line := range strings.Split(diff, "\n") {
+		// Track current file from +++ header
+		if strings.HasPrefix(line, "+++ b/") {
+			currentFile = strings.TrimPrefix(line, "+++ b/")
+			if result.files[currentFile] == nil {
+				result.files[currentFile] = make(map[int]bool)
+			}
+			continue
+		}
+		if strings.HasPrefix(line, "+++ /dev/null") {
+			currentFile = ""
+			continue
+		}
+
+		// Parse hunk header: @@ -old,count +new,count @@
+		if strings.HasPrefix(line, "@@") && currentFile != "" {
+			// Extract the +N part
+			parts := strings.Split(line, "+")
+			if len(parts) >= 2 {
+				numStr := strings.Split(parts[1], ",")[0]
+				n, err := strconv.Atoi(numStr)
+				if err == nil {
+					newLine = n
+				}
+			}
+			continue
+		}
+
+		if currentFile == "" {
+			continue
+		}
+
+		// Count lines in hunk
+		if strings.HasPrefix(line, "+") || strings.HasPrefix(line, " ") {
+			result.files[currentFile][newLine] = true
+			newLine++
+		} else if strings.HasPrefix(line, "-") {
+			// Removed lines don't advance new line counter
+			continue
+		}
+	}
+
+	return result
+}

gitea/diff_test.go

@@ -0,0 +1,75 @@
+package gitea
+
+import (
+	"testing"
+)
+
+func TestParseDiffLineRanges(t *testing.T) {
+	diff := `diff --git a/main.go b/main.go
+index abc1234..def5678 100644
+--- a/main.go
++++ b/main.go
+@@ -10,6 +10,8 @@ func main() {
+ 	fmt.Println("hello")
++	fmt.Println("new line 11")
++	fmt.Println("new line 12")
+ 	fmt.Println("existing")
+ }
+@@ -30,4 +32,5 @@ func other() {
+ 	return nil
++	// added at line 33
+ }
+diff --git a/util.go b/util.go
+new file mode 100644
+--- /dev/null
++++ b/util.go
+@@ -0,0 +1,5 @@
++package main
++
++func helper() string {
++	return "hi"
++}
+`
+
+	ranges := ParseDiffNewLines(diff)
+
+	// main.go should have lines 10-17 (first hunk) and 32-36 (second hunk)
+	if !ranges.Contains("main.go", 11) {
+		t.Error("expected main.go:11 to be in diff")
+	}
+	if !ranges.Contains("main.go", 12) {
+		t.Error("expected main.go:12 to be in diff")
+	}
+	if !ranges.Contains("main.go", 10) {
+		t.Error("expected main.go:10 to be in diff (context line)")
+	}
+	if !ranges.Contains("main.go", 33) {
+		t.Error("expected main.go:33 to be in diff")
+	}
+	if ranges.Contains("main.go", 25) {
+		t.Error("main.go:25 should NOT be in diff")
+	}
+
+	// util.go is entirely new, lines 1-5
+	if !ranges.Contains("util.go", 1) {
+		t.Error("expected util.go:1 to be in diff")
+	}
+	if !ranges.Contains("util.go", 5) {
+		t.Error("expected util.go:5 to be in diff")
+	}
+	if ranges.Contains("util.go", 6) {
+		t.Error("util.go:6 should NOT be in diff")
+	}
+
+	// Unknown file
+	if ranges.Contains("unknown.go", 1) {
+		t.Error("unknown.go should not be in diff")
+	}
+}
+
+func TestParseDiffNewLines_Empty(t *testing.T) {
+	ranges := ParseDiffNewLines("")
+	if ranges.Contains("any.go", 1) {
+		t.Error("empty diff should contain nothing")
+	}
+}

gitea/post_review_comments_test.go

@@ -0,0 +1,88 @@
+package gitea
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestPostReview_WithComments(t *testing.T) {
+	var gotPayload struct {
+		Body     string `json:"body"`
+		Event    string `json:"event"`
+		Comments []struct {
+			Path        string `json:"path"`
+			NewPosition int64  `json:"new_position"`
+			Body        string `json:"body"`
+		} `json:"comments"`
+	}
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewDecoder(r.Body).Decode(&gotPayload)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(200)
+		json.NewEncoder(w).Encode(map[string]any{
+			"id":   99,
+			"body": gotPayload.Body,
+			"user": map[string]any{"login": "bot"},
+		})
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL, "test-token")
+	comments := []ReviewComment{
+		{Path: "main.go", NewPosition: 42, Body: "[MAJOR] Something bad"},
+		{Path: "util.go", NewPosition: 10, Body: "[MINOR] Style issue"},
+	}
+
+	_, err := client.PostReview(context.Background(), "owner", "repo", 1, "REQUEST_CHANGES", "summary", comments)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if len(gotPayload.Comments) != 2 {
+		t.Fatalf("expected 2 comments, got %d", len(gotPayload.Comments))
+	}
+	if gotPayload.Comments[0].Path != "main.go" {
+		t.Errorf("expected path main.go, got %s", gotPayload.Comments[0].Path)
+	}
+	if gotPayload.Comments[0].NewPosition != 42 {
+		t.Errorf("expected new_position 42, got %d", gotPayload.Comments[0].NewPosition)
+	}
+	if gotPayload.Comments[1].Body != "[MINOR] Style issue" {
+		t.Errorf("unexpected body: %s", gotPayload.Comments[1].Body)
+	}
+}
+
+func TestPostReview_NilComments(t *testing.T) {
+	var gotPayload map[string]any
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewDecoder(r.Body).Decode(&gotPayload)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(200)
+		json.NewEncoder(w).Encode(map[string]any{
+			"id":   100,
+			"body": "test",
+			"user": map[string]any{"login": "bot"},
+		})
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL, "test-token")
+	_, err := client.PostReview(context.Background(), "owner", "repo", 1, "APPROVED", "all good", nil)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// With nil comments, the field should be omitted (omitempty)
+	comments, ok := gotPayload["comments"]
+	if ok && comments != nil {
+		arr, isArr := comments.([]any)
+		if isArr && len(arr) > 0 {
+			t.Error("expected no comments in payload when nil passed")
+		}
+	}
+}