fix: render per-comment file line instead of thread-level location

tests/render_json_tests.rs

@@ -37,6 +37,8 @@ fn model_json_roundtrip() {
                 id: 100,
                 user: "reviewer".into(),
                 created_at: "2026-04-08T12:00:00Z".into(),
+                path: Some("src/main.rs".into()),
+                line: Some(10),
                 body: "hello".into(),
             },
             replies: vec![],

tests/render_markdown_tests.rs

@@ -50,12 +50,16 @@ fn render_markdown_includes_expected_sections_and_preserves_comment_markdown() {
                 id: 11,
                 user: "bob".into(),
                 created_at: "2026-04-08T11:01:00Z".into(),
+                path: Some("src/main.rs".into()),
+                line: Some(9),
                 body: "```rs\nlet x = 1;\n```".into(),
             },
             replies: vec![CommentItem {
                 id: 12,
                 user: "alice".into(),
                 created_at: "2026-04-08T11:02:00Z".into(),
+                path: Some("src/main.rs".into()),
+                line: Some(12),
                 body: "looks good".into(),
             }],
         }],
@@ -69,7 +73,9 @@ fn render_markdown_includes_expected_sections_and_preserves_comment_markdown() {
     assert!(md.contains("## Diff Stat"));
     assert!(md.contains("## Review 1 (COMMENT)"));
     assert!(md.contains("### Comment 7.1"));
+    assert!(md.contains("src/main.rs:9"));
     assert!(md.contains("### Reply 7.1.1"));
+    assert!(md.contains("src/main.rs:12"));
     assert!(md.contains("````md"));
     assert!(md.contains("```rs\nlet x = 1;\n```"));
     assert!(md.contains("looks good"));
@@ -107,6 +113,8 @@ fn render_markdown_uses_minimal_fence_for_plain_text() {
                 id: 1,
                 user: "bob".into(),
                 created_at: "2026-04-08T11:00:00Z".into(),
+                path: None,
+                line: None,
                 body: body.into(),
             },
             replies: vec![],