refactor: extract shared utilities, protocol constants, and retry loop

Phase 3: provider-retry.ts — shared Claude rotation loop (SSOT)
  - retryClaudeWithRotation extracted from message-agent-executor + task-scheduler
  - ~200 lines of duplicated retry logic removed

Phase 4: types.ts — AgentOutputPhase + VisiblePhase unified
Phase 5: types.ts — AgentConfig extended with claudeThinking/claudeThinkingBudget

Utilities (utils.ts):
  - getErrorMessage: 14 occurrences of instanceof Error pattern → 1 function
  - readJsonFile/writeJsonFile: 19 occurrences of JSON+fs pattern → 2 functions
  - fetchWithTimeout: 3 occurrences of AbortController pattern → 1 function
  - formatElapsedKorean: deduplicated from task-watch-status + message-turn-controller

Protocol (agent-protocol.ts):
  - OUTPUT_START/END_MARKER centralized (runners keep local copies with SSOT reference)
  - IMAGE_TAG_RE, IPC constants documented

Runner: show "대화 요약 중..." progress message during auto-compact

Net: -137 lines, 354/354 tests passing

src/task-watch-status.ts

@@ -1,5 +1,6 @@
 import { TIMEZONE } from './config.js';
 import type { ScheduledTask } from './types.js';
+import { formatElapsedKorean } from './utils.js';
 
 export type WatcherStatusPhase =
   | 'checking'
@@ -65,16 +66,7 @@ function formatElapsedLabel(
     0,
     new Date(checkedAtIso).getTime() - new Date(startedAtIso).getTime(),
   );
-  const totalSeconds = Math.floor(elapsedMs / 1000);
-  const hours = Math.floor(totalSeconds / 3600);
-  const minutes = Math.floor((totalSeconds % 3600) / 60);
-  const seconds = totalSeconds % 60;
-
-  const parts: string[] = [];
-  if (hours > 0) parts.push(`${hours}시간`);
-  if (minutes > 0) parts.push(`${minutes}분`);
-  parts.push(`${seconds}초`);
-  return parts.join(' ');
+  return formatElapsedKorean(elapsedMs);
 }
 
 export function renderWatchCiStatusMessage(args: {