fix(aider-watch): code-review fixes (4 issues)

1. aiderw: session_end 補 model+cwd (AI Router feedback loop 修通)
2. repository: model_stats_since SQL 改 COALESCE(session_end, session_start) model
3. aider_event_service: classify_severity 移除 error_count 觸發告警（防假陽性）
4. worker: run_aider_event_processor_loop 包 proc.start() try/except（防靜默崩潰）

2026-04-20 @ Asia/Taipei

scripts/aider_watch_client/aider_watch_client/aiderw.py

@@ -157,6 +157,7 @@ def main(argv: list[str] | None = None) -> int:
                         "context_50chars": stdout_text[-50:]},
         })
 
+    banner = parse_stdout_banner(stdout_text)
     events_tail.append({
         "ts": _now_iso(), "session_id": sid, "host": host,
         "type": "session_end",
@@ -166,7 +167,9 @@ def main(argv: list[str] | None = None) -> int:
                     "files_changed": len([e for e in events_tail
                                            if e["type"] == "file_edit"]),
                     "error_count": error_count[0],
-                    "exit_code": exit_code},
+                    "exit_code": exit_code,
+                    "model": banner.get("model", "unknown"),
+                    "cwd": str(cwd)},
     })
 
     if events_tail: