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/types.ts

@@ -5,10 +5,22 @@ export interface AgentConfig {
   codexEffort?: string;
   claudeModel?: string;
   claudeEffort?: string;
+  claudeThinking?: 'adaptive' | 'enabled' | 'disabled';
+  claudeThinkingBudget?: number;
 }
 
 export type AgentType = 'claude-code' | 'codex';
 
+/** Phase of agent output as emitted by the runner. */
+export type AgentOutputPhase =
+  | 'progress'
+  | 'final'
+  | 'tool-activity'
+  | 'intermediate';
+
+/** Phase as visible in the UI (mapped from AgentOutputPhase). */
+export type VisiblePhase = 'silent' | 'progress' | 'final';
+
 export interface RegisteredGroup {
   name: string;
   folder: string;