ops(triage): PR-4B-Diagnose — exception logging 강화 (type/repr/exc_info)

Layer 1 root cause 진단을 위해 classify_worker.py:595 의 exception logging
을 lazy formatting + exc_info=True 로 강화. f-string 1줄 → 5줄 block.
- type=%s: exception class name (TimeoutError/JSONDecodeError/ValueError/etc.)
- repr=%r: full exception state
- exc_info=True: traceback 까지 capture (wrapper 정확 지점 추적)

본 PR scope = Diagnose only. Layer 1 specific fix (H1/H2/H3/H4) + Layer 2
escalate path ai_event_kind fallback set 은 별 PR queue.

plan: ~/.claude/plans/c-1-pr-infra-drift-1-phase-1b-linear-frost.md
backup: app/workers/classify_worker.py.pre-4b-diagnose.20260517

app/workers/classify_worker.py

@@ -592,7 +592,13 @@ async def _run_tier_triage(client: AIClient, doc: Document, session: AsyncSessio
     try:
         raw_triage = await client.call_triage(prompt)
     except Exception as exc:
-        logger.warning(f"[triage] 4B 호출 실패 id={document_id}: {exc}")
+        logger.warning(
+            "[triage] 4B 호출 실패 id=%s type=%s repr=%r",
+            document_id,
+            type(exc).__name__,
+            exc,
+            exc_info=True,
+        )
         parse_error = "call_failed"
         raw_triage = ""