fix: 全站 ruff 清零 — 77 errors → 0

Fixes:
- F821: install.py site_url 未定义(NameError)、sync_v2.py os 未导入、script_jobs.py LOG f-string
- F401: 移除 22 个未使用导入（models/__init__.py、install.py、auth.py 等）
- B904: 20 个 except 块 raise 添加 from e/from None
- S110: 20 个有意的 try-except-pass 添加 noqa 注释（SSH清理/DDL幂等/WS断连）
- B007: 3 个未使用循环变量重命名（dirs→_dirs、server_id→_server_id）
- F541: 3 个无占位符 f-string 修正
- F841: auth.py 未使用 ip_address 变量移除
- S105: auth_service.py Redis key prefix 误报 noqa
- B023: script_execution_flush.py 循环变量绑定修复

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/infrastructure/ssh/asyncssh_pool.py

@@ -74,10 +74,10 @@ class AsyncSSHPool:
                 pass
 
         async with self._lock:
-            for server_id, pooled in self._pool.items():
+            for _server_id, pooled in self._pool.items():
                 try:
                     pooled.conn.close()
-                except Exception:
+                except Exception:  # noqa: S110 — best-effort cleanup
                     pass
             self._pool.clear()
         logger.info("AsyncSSH pool stopped — all connections closed")
@@ -118,7 +118,7 @@ class AsyncSSHPool:
                 # Close our new connection, reuse the existing one
                 try:
                     conn.close()
-                except Exception:
+                except Exception:  # noqa: S110 — best-effort cleanup
                     pass
                 pooled.ref_count += 1
                 pooled.last_used = time.monotonic()
@@ -153,7 +153,7 @@ class AsyncSSHPool:
             if pooled:
                 try:
                     pooled.conn.close()
-                except Exception:
+                except Exception:  # noqa: S110 — best-effort cleanup
                     pass
                 logger.debug(f"Force-closed SSH connection: server={server_id}")
 
@@ -190,7 +190,7 @@ class AsyncSSHPool:
             conn = await asyncssh.connect(**connect_kwargs)
             return conn
         except asyncssh.Error as e:
-            raise ConnectionError(f"SSH connection failed to {server.domain}:{server.port}: {e}")
+            raise ConnectionError(f"SSH connection failed to {server.domain}:{server.port}: {e}") from e
 
     async def _evict_one(self) -> bool:
         """Evict the oldest idle connection from the pool.
@@ -209,7 +209,7 @@ class AsyncSSHPool:
             pooled = self._pool.pop(oldest_idle)
             try:
                 pooled.conn.close()
-            except Exception:
+            except Exception:  # noqa: S110 — best-effort cleanup
                 pass
             logger.debug(f"Evicted idle SSH connection: server={oldest_idle}")
             return True
@@ -233,7 +233,7 @@ class AsyncSSHPool:
                         pooled = self._pool.pop(server_id)
                         try:
                             pooled.conn.close()
-                        except Exception:
+                        except Exception:  # noqa: S110 — best-effort cleanup
                             pass
 
                     if to_remove: