fix(lint): resolve all 37 flake8 issues

- Remove 7 unused imports (F401)
- Fix 4 f-strings without placeholders (F541)
- Fix indentation and blank line issues (E127/E302/E402)
- Remove trailing whitespace on 22 blank lines (W293)

Pure formatting changes, no logic modifications.

src/daemon/task_handler.py

@@ -7,7 +7,7 @@ from __future__ import annotations
 import logging
 import os
 from pathlib import Path
-from typing import Dict, List, Optional
+from typing import Dict, Optional
 
 from src.daemon.base_task_handler import BaseTaskHandler, VerifyResult
 from src.daemon.prompt_composer import PromptComposer, PromptContext
@@ -182,7 +182,7 @@ class TaskConstraintsSection:
 
 class TaskHandler(BaseTaskHandler):
     """黑板标准任务 handler。
-    
+
     - verify: 三信号检查（output / comment / terminal status）
     - 成功 → review
     - 失败 → 保持 working，让 ticker 重试
@@ -198,7 +198,7 @@ class TaskHandler(BaseTaskHandler):
     def post_complete(self, task_id: str, agent_id: str,
                       outcome: str, db_path: Path) -> None:
         """Task on_complete：区分 executor 和 review。
-        
+
         executor: 基类统一流程（crash → verify → mark review）
         review: handle_review_complete（读 verdict → done/keep review）
         """