refactor(main): IPC 채널 SSOT 일원화 + AppConfig 타입 강화 (WS2)

- ipc-channels.ts SSOT에 9개 그룹/키 추가: INSTRUCTION, SYSTEM_AUDIO,
  POPUP_RESULT/HISTORY/COMMAND/CAPTION, VOICE_PARTIAL, CLIPBOARD, APP,
  VOICE_CONVERSATION.FINISH_LISTENING
- WindowManager/handlers/bootstrap 하드코딩 채널 -> IPC_CHANNELS 교체.
  불일치 4건(result:* vs window:tip*)은 preload 재검증 후 SSOT로 통일.
  notifyRenderer channel: string -> IPCChannel 타입 좁힘.
- AppConfig에 7개 누락 키 추가(customInstructions, llmChains,
  voiceCommandRules, voiceCommandsEnabled, activeInstructionId,
  activeChainId, captionAudioSource) -> as never 16건 제거.
- ChainService/CustomInstructionService/WindowManager dynamic require -> static import.
- services/index.ts 데드 레지스트리 제거 (import 0건).
SKIP: ipcSuccess/ipcError 헬퍼 통일, catch 패턴(별도)
정책: docs/REFACTOR_POLICY.md DP2, DP9

apps/desktop/src/main/services/MeetingModeService.ts

@@ -145,9 +145,8 @@ class MeetingModeService extends EventEmitter {
 
     // 회의 모드는 마이크 캡처 강제 — ConfigService 값도 임시 변경
     // (CaptionService.start()가 ConfigService에서 다시 읽기 때문)
-    type AppConfigKey = keyof import('@d3ro/core/types').AppConfig
-    const prevAudioSource = configGet('captionAudioSource' as AppConfigKey) as unknown as string
-    configSet('captionAudioSource' as AppConfigKey, 'mic' as never)
+    const prevAudioSource = configGet('captionAudioSource')
+    configSet('captionAudioSource', 'mic')
 
     try {
       await captionService.start()
@@ -156,12 +155,12 @@ class MeetingModeService extends EventEmitter {
       hideCaptionOverlay()
       // ConfigService 원래 값 복원
       if (prevAudioSource) {
-        configSet('captionAudioSource' as AppConfigKey, prevAudioSource as never)
+        configSet('captionAudioSource', prevAudioSource)
       }
     } catch (err) {
       // ConfigService 원래 값 복원
       if (prevAudioSource) {
-        configSet('captionAudioSource' as AppConfigKey, prevAudioSource as never)
+        configSet('captionAudioSource', prevAudioSource)
       }
       // 시작 실패 시 복원
       captionService.off('segment', this._segmentHandler)