review(회차1): nit 3건 — 의도 문서화 (best-effort IO 의도 + bar invariant + display join)

회차 1 actionable 모두 동작 변경 없음, 의도 명시.

- progress.rs handle_human: doc-comment 한 단락 — `let _ = writeln!`
  의 IO error swallow 와 `bar.as_ref()` None 분기 silent skip 의
  두 best-effort 의도 + §2.4a ordering invariant (ScanStarted 가
  bar 를 lazy 초기화) 명시.
- main.rs Cmd::Ingest: `let _ = display_handle.join();` 위에 한 줄
  trailing comment — Result<Result<(), anyhow::Error>, Box<dyn Any>>
  를 모두 discard 하는 이유 (display thread 의 에러 / panic 이
  ingest exit code 에 영향 없어야 함).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-cli/src/progress.rs

@@ -87,6 +87,15 @@ impl ProgressDisplay {
         }
     }
 
+    /// Render an event in human mode. **Best-effort**: every
+    /// `writeln!` into stderr swallows IO errors (`let _ = ...`)
+    /// because the progress display must not fail the ingest run if
+    /// the terminal is closed mid-stream. Likewise the
+    /// `self.bar.as_ref()` / `as_mut()` branches treat a missing
+    /// bar as silent skip — the bar is initialized lazily in the
+    /// `ScanStarted` arm and §2.4a's ordering invariant
+    /// (`ScanStarted` < everything else) guarantees it is `Some` by
+    /// the time later events arrive.
     fn handle_human(&mut self, event: &IngestEvent, tty: bool) -> anyhow::Result<()> {
         match event {
             IngestEvent::ScanStarted { root } => {