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/api/settings.py

@@ -19,7 +19,7 @@ from server.infrastructure.database.push_schedule_repo import PushScheduleReposi
 from server.infrastructure.database.password_preset_repo import PasswordPresetRepositoryImpl
 from server.infrastructure.database.ssh_key_preset_repo import SshKeyPresetRepositoryImpl
 from server.infrastructure.database.audit_log_repo import AuditLogRepositoryImpl
-from server.domain.models import Setting, PushSchedule, PushRetryJob, PasswordPreset, SshKeyPreset, AuditLog, Admin
+from server.domain.models import PushSchedule, PushRetryJob, PasswordPreset, SshKeyPreset, AuditLog, Admin
 
 from sqlalchemy.ext.asyncio import AsyncSession
 
@@ -327,7 +327,7 @@ async def reveal_preset(
     try:
         plaintext = decrypt_value(preset.encrypted_pw)
     except ValueError:
-        raise HTTPException(status_code=500, detail="解密失败")
+        raise HTTPException(status_code=500, detail="解密失败") from None
 
     audit_repo = AuditLogRepositoryImpl(db)
     await audit_repo.create(AuditLog(
@@ -472,7 +472,7 @@ async def reveal_ssh_key_preset(
     try:
         plaintext = decrypt_value(preset.encrypted_private_key)
     except ValueError:
-        raise HTTPException(status_code=500, detail="解密失败")
+        raise HTTPException(status_code=500, detail="解密失败") from None
 
     audit_repo = AuditLogRepositoryImpl(db)
     await audit_repo.create(AuditLog(
@@ -689,7 +689,7 @@ async def telegram_get_chats(
     except HTTPException:
         raise
     except Exception as e:
-        raise HTTPException(status_code=502, detail=f"请求失败: {e}")
+        raise HTTPException(status_code=502, detail=f"请求失败: {e}") from e
 
     # Extract unique chats
     seen: set[int] = set()
@@ -748,11 +748,11 @@ async def parse_subscription(
             raise HTTPException(status_code=400, detail=f"订阅链接返回 HTTP {resp.status_code}")
         raw = resp.text
     except httpx.TimeoutException:
-        raise HTTPException(status_code=400, detail="请求订阅链接超时（15s）")
+        raise HTTPException(status_code=400, detail="请求订阅链接超时（15s）") from None
     except HTTPException:
         raise
     except Exception as e:
-        raise HTTPException(status_code=400, detail=f"获取订阅失败: {e}")
+        raise HTTPException(status_code=400, detail=f"获取订阅失败: {e}") from e
 
     hosts = parse_subscription_content(raw)
     if not hosts:
@@ -914,7 +914,7 @@ async def get_ip_allowlist(
 ):
     """Return full allowlist state."""
     from server.config import settings as _settings
-    from server.background.ip_allowlist_refresh import get_last_refresh_time, get_subscription_count
+    from server.background.ip_allowlist_refresh import get_last_refresh_time
 
     allowlist_on = (_settings.LOGIN_ALLOWLIST_ENABLED or "false").lower() in ("true","1","yes","on")
     sub_ips_raw = _settings.LOGIN_SUBSCRIPTION_IPS or ""