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_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")
 	}