feat: 3.2.17中途变更处理(git驱动) + 3.2.9a Worker git强制 + 3.2.5 Phase7 squash merge + Arc git初始化检测

- 新增 ChangeClassifier（爆炸半径分类：IMPLEMENTATION/INTERFACE/GLOBAL_CONSTRAINT）
- 新增 ImpactPropagator（BFS影响传播：IMPACTED/BOUNDARY/SAFE差异化标记）
- task_graph.py：invalidate_by_adr()差异化失效 + CascadeReport扩展字段（向后兼容）
- eng_mode.py：三阶段差异化流程（分类→传播→失效→git操作→验证任务→重规划）
- eng_mode.py：_git_squash_merge_and_tag() + Phase 7 集成
- do_mode.py：_ensure_all_committed() Worker git操作强制
- adr_watcher.py：内容快照 + get_content_for_classification()
- events.py：ADR_CLASSIFIED/IMPACT_PROPAGATED/BOUNDARY_VERIFICATION_GENERATED
- partial_replanner.py：replan_with_constraints() + generate_verification_tasks()
- project_bootstrap.py：ensure_git_initialized() Arc规划前检测
- test_p1_21_phase2.py：21个新测试，95个全量测试0失败

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/air_runtime/events.py

@@ -41,7 +41,10 @@ WORKER_TIMEOUT = "worker.timeout"
 WORKTREE_MERGE_CONFLICT = "worktree.merge.conflict"
 ARC_REPLANNED = "arc.replanned"
 ADR_CHANGE_DETECTED = "adr.change.detected"
+ADR_CLASSIFIED = "adr.classified"
 ADR_INVALIDATION = "adr.invalidation"
+IMPACT_PROPAGATED = "impact.propagated"
+BOUNDARY_VERIFICATION_GENERATED = "boundary.verification.generated"
 ADR_UNFREEZED = "adr.unfreezed"
 LOCK_ACQUIRED = "lock.acquired"
 LOCK_RELEASED = "lock.released"