fix(lint): 修复 PR #14 引入的 lint 回退 (119→0)

PR #14 从旧分支复制文件导致回退了 PR #10 的 lint 修复。
修复内容:
- autoflake 移除未使用导入/变量
- autopep8 修复缩进/空格
- 手动修复 F821(pathlib→Path), F541(f-string), F841(未使用变量)
- 所有修复均通过 flake8 --max-line-length=120 --extend-ignore=E501 检查 (0 errors)

src/main.py

@@ -1,6 +1,13 @@
 """v2.6 主入口 - FastAPI + Daemon ticker 共享 asyncio event loop"""
 
 from __future__ import annotations
+from src.api.toolchain_routes import router as toolchain_router
+from src.api.mail_routes import router as mail_router
+from src.api.sse_routes import router as sse_router
+from src.api.project_routes import router as project_router
+from src.api.daemon_routes import router as daemon_router
+from src.api.checkpoint_routes import router as checkpoint_router
+from src.api.blackboard_routes import router as blackboard_router
 
 import logging
 from contextlib import asynccontextmanager
@@ -131,7 +138,8 @@ async def lifespan(app: FastAPI):
     counter = ActiveAgentCounter(
         max_global=daemon_config.get("max_global_agents", 5),
         max_per_session=daemon_config.get("max_per_session", 1),
-        max_concurrent_sessions=daemon_config.get("max_concurrent_sessions", 3),
+        max_concurrent_sessions=daemon_config.get(
+            "max_concurrent_sessions", 3),
         default_cooldown_seconds=daemon_config.get("cooldown_seconds", 120),
     )
     # BootstrapBuilder（L2 四段式引擎注入层，v2.1）
@@ -181,7 +189,10 @@ async def lifespan(app: FastAPI):
         spawner=spawner,
         counter=counter,
         db_path=default_db_path,
-        guardrails=GuardrailEngine(config_path=Path(__file__).parent.parent / "config" / "guardrails.yaml"),
+        guardrails=GuardrailEngine(
+            config_path=Path(__file__).parent.parent /
+            "config" /
+            "guardrails.yaml"),
     )
 
     # ── 集成模块 ──
@@ -191,7 +202,7 @@ async def lifespan(app: FastAPI):
     )
 
     # ExperienceDistiller（经验自动蒸馏）
-    experience_config = config.get("experience", {})
+    config.get("experience", {})
     experience_distiller = ExperienceDistiller(
         store=ExperienceStore(store_path=DATA_ROOT / "experiences.jsonl"),
     )
@@ -252,13 +263,6 @@ app.add_middleware(
 # API 路由注册
 # ---------------------------------------------------------------------------
 
-from src.api.blackboard_routes import router as blackboard_router
-from src.api.checkpoint_routes import router as checkpoint_router
-from src.api.daemon_routes import router as daemon_router
-from src.api.project_routes import router as project_router
-from src.api.sse_routes import router as sse_router
-from src.api.mail_routes import router as mail_router
-from src.api.toolchain_routes import router as toolchain_router
 
 app.include_router(blackboard_router)
 app.include_router(checkpoint_router)
@@ -300,16 +304,17 @@ async def list_projects_compat():
 DIST_DIR = Path(__file__).parent / "frontend" / "dist"
 if DIST_DIR.exists():
     # v3.1: 缓存策略 - HTML 不缓存（确保新版本生效），JS/CSS 长缓存（Vite content hash 已处理）
-    import mimetypes
     _static_app = StaticFiles(directory=str(DIST_DIR), html=True)
-    
+
     class CachedStaticFiles:
         """包装 StaticFiles，添加 Cache-Control 头"""
+
         def __init__(self, app):
             self._app = app
-        
+
         async def __call__(self, scope, receive, send):
             original_send = send
+
             async def patched_send(message):
                 if message.get("type") == "http.response.start":
                     headers = dict(message.get("headers", []))
@@ -321,5 +326,5 @@ if DIST_DIR.exists():
                     message["headers"] = list(headers.items())
                 await original_send(message)
             await self._app(scope, receive, patched_send)
-    
+
     app.mount("/", CachedStaticFiles(_static_app), name="frontend")