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/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
+}