fix: v3.0→HEAD review 修复 — handler 注册 + review verdict + skill 全文注入

基于庞统+司马懿背靠背 review，修复 6 个问题：

P0 致命：
- A1: _legacy_on_complete 补回 review verdict 处理（approved→done，非 approved→@mention assignee）
- A2: 添加 TaskTypeRegistry.register() 启动初始化（注册 Task/Mail/Toolchain handler）

P1 中等：
- B11-1: RoleSkillSection 从索引提示改为全文注入（对齐设计 §2.3 + BootstrapBuilder 行为）
- A8: retry prompt is_mail 硬编码改走 TaskTypeRegistry handler 判断

P2 低：
- _mail_* 4 个方法添加 DEPRECATED 注释
- ticker.py handler check_completion 代码块缩进对齐（28→24 空格）

测试：394 passed, 0 failed
Review reports: docs/design/review-v3-vs-head-{pangtong,simayi}.md

src/main.py

@@ -21,6 +21,10 @@ from fastapi.staticfiles import StaticFiles
 
 from src.blackboard.registry import ProjectRegistry
 from src.daemon.ticker import Ticker
+from src.daemon.task_handler import TaskHandler
+from src.daemon.mail_handler import MailHandler
+from src.daemon.toolchain_handler import ToolchainHandler
+from src.daemon.task_type_registry import TaskTypeRegistry
 from src.daemon.spawner import AgentSpawner
 from src.daemon.bootstrap import BootstrapBuilder
 from src.daemon.dispatcher import Dispatcher
@@ -214,6 +218,11 @@ async def lifespan(app: FastAPI):
         watch_interval=inbox_config.get("watch_interval", 1.0),
     )
 
+    # [Step 5] 注册 TaskType handler（必须在 ticker 启动前）
+    TaskTypeRegistry.register(TaskHandler())
+    TaskTypeRegistry.register(MailHandler())
+    TaskTypeRegistry.register(ToolchainHandler())
+
     ticker = Ticker(
         registry=registry,
         tick_interval=tick_interval,