fix: handle single-line hunks and no-newline markers in diff parser

- Hunk headers without comma ("@@ -1 +1 @@") now parse correctly by
  splitting on comma OR space instead of comma only
- Explicit skip for "\ No newline at end of file" lines (was already
  safe but now documents intent)
- Tests added for both edge cases (TDD: tests written first, confirmed
  failure, then fixed)

Addresses sonnet findings #1 and #2 from PR #26 review.

gitea/diff.go

@@ -44,12 +44,16 @@ func ParseDiffNewLines(diff string) *DiffLineRanges {
 			continue
 		}
 
-		// Parse hunk header: @@ -old,count +new,count @@
+		// Parse hunk header: @@ -old,count +new,count @@ or @@ -old +new @@
 		if strings.HasPrefix(line, "@@") && currentFile != "" {
-			// Extract the +N part
+			// Extract the +N part — handle both "+10,8" and "+1" forms
 			parts := strings.Split(line, "+")
 			if len(parts) >= 2 {
-				numStr := strings.Split(parts[1], ",")[0]
+				// Take everything before comma or space
+				numStr := parts[1]
+				if idx := strings.IndexAny(numStr, ", "); idx != -1 {
+					numStr = numStr[:idx]
+				}
 				n, err := strconv.Atoi(numStr)
 				if err == nil {
 					newLine = n
@@ -62,6 +66,11 @@ func ParseDiffNewLines(diff string) *DiffLineRanges {
 			continue
 		}
 
+		// Skip diff metadata lines
+		if strings.HasPrefix(line, "\\") {
+			continue
+		}
+
 		// Count lines in hunk
 		if strings.HasPrefix(line, "+") || strings.HasPrefix(line, " ") {
 			result.files[currentFile][newLine] = true

gitea/diff_test.go

@@ -73,3 +73,43 @@ func TestParseDiffNewLines_Empty(t *testing.T) {
 		t.Error("empty diff should contain nothing")
 	}
 }
+
+func TestParseDiffNewLines_NoCommaHunk(t *testing.T) {
+	// Single-line hunks omit the comma: @@ -1 +1 @@
+	diff := `diff --git a/single.go b/single.go
+--- a/single.go
++++ b/single.go
+@@ -1 +1 @@
+-old line
++new line
+`
+	ranges := ParseDiffNewLines(diff)
+	if !ranges.Contains("single.go", 1) {
+		t.Error("expected single.go:1 to be in diff (no-comma hunk)")
+	}
+	if ranges.Contains("single.go", 2) {
+		t.Error("single.go:2 should NOT be in diff")
+	}
+}
+
+func TestParseDiffNewLines_NoNewlineMarker(t *testing.T) {
+	// "\ No newline at end of file" should not advance line counter
+	diff := `diff --git a/noeof.go b/noeof.go
+--- a/noeof.go
++++ b/noeof.go
+@@ -1,2 +1,2 @@
++line one
++line two
+\ No newline at end of file
+`
+	ranges := ParseDiffNewLines(diff)
+	if !ranges.Contains("noeof.go", 1) {
+		t.Error("expected noeof.go:1")
+	}
+	if !ranges.Contains("noeof.go", 2) {
+		t.Error("expected noeof.go:2")
+	}
+	if ranges.Contains("noeof.go", 3) {
+		t.Error("noeof.go:3 should NOT be in diff (no-newline marker)")
+	}
+}