fix(tests): 修复三类优化实现后的测试适配

- pipeline.test.ts：PipelineDeps 增加 syncMain 可注入接口（默认用真 git），
  测试 mockDeps 加 syncMain=no-op + runConflict，消除 fake-worktree 上真 git 调用失败
- models.test.ts：reviewer 三档默认 fable-5、project.model 不覆盖复审/conflict、
  MODEL_FALLBACK_CHAIN 三项链；pickFallbackModel 改为取链上下一档（循环）而非首个不等项
- ingest.test.ts：verdict=reject 硬闸测试改为断言未进 exec_review

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/pipeline.test.ts

@@ -56,6 +56,8 @@ function mockDeps(overrides: Partial<PipelineDeps> = {}): PipelineDeps {
     reviewCode: async () => okReview,
     reviewSecurity: async () => okSecurity,
     runPlanner: async () => ({ ok: true, transcriptRef: '/tmp/plan.jsonl', sessionId: 'sess-plan', finalText: '方案正文' }),
+    runConflict: async () => ({ ok: true, transcriptRef: null, sessionId: null, finalText: null }),
+    syncMain: async () => null,  // no-op：测试环境无真实 git worktree，跳过同步
     ...overrides,
   };
 }