refactor: MoA uses lightweight API references + SDK arbiter as aggregator

Instead of spawning separate processes or using OpenRouter, MoA now:
- Queries external API models (Kimi, GLM) in parallel for opinions
- Injects opinions into the SDK arbiter's prompt
- The existing subscription-based arbiter aggregates all perspectives

No extra SDK processes, no OpenRouter dependency. Per-model config via
MOA_REF_MODELS + MOA_{NAME}_MODEL/BASE_URL/API_KEY env vars.

src/message-runtime.test.ts

@@ -23,7 +23,11 @@ vi.mock('./config.js', () => ({
   isClaudeService: vi.fn(() => true),
   isReviewService: vi.fn(() => false),
   isSessionCommandSenderAllowed: vi.fn(() => false),
-  getMoaConfig: vi.fn(() => ({ enabled: false, referenceModels: [], aggregator: {} })),
+  getMoaConfig: vi.fn(() => ({
+    enabled: false,
+    referenceModels: [],
+    aggregator: {},
+  })),
   TIMEZONE: 'Asia/Seoul',
 }));