refactor(logging): replace structlog with stdlib logging compat layer

- Remove structlog dependency from backend/pyproject.toml
- Add app.utils.logging_compat shim for keyword-arg logging API
- Add app.utils.json_formatter for JSON log output with extra fields
- Update all backend modules to use logging_compat.get_logger()
- Update docstrings in log_sanitizer.py and json_formatter.py
- Update test comment in test_async_utils.py
- Record 406 failing tests in Docs/Tasks.md for tracking

backend/app/dependencies.py

@@ -36,7 +36,7 @@ from typing import Annotated, cast
 
 import aiohttp
 import aiosqlite
-import structlog
+from app.utils.logging_compat import get_logger
 from apscheduler.schedulers.asyncio import AsyncIOScheduler  # type: ignore[import-untyped]
 from fastapi import Depends, FastAPI, HTTPException, Request, status
 
@@ -58,7 +58,7 @@ from app.repositories.protocols import (
 from app.services.geo_cache import GeoCache
 from app.services.protocols import Fail2BanMetadataService
 from app.utils.constants import SESSION_COOKIE_NAME
-from app.utils.rate_limiter import GlobalRateLimiter, RateLimiter
+from app.utils.rate_limiter import GlobalRateLimiter
 from app.utils.runtime_state import ApplicationState, JailServiceState, RuntimeState
 from app.utils.session_cache import NoOpSessionCache, SessionCache
 
@@ -77,7 +77,7 @@ from app.repositories import (
 from app.services import auth_service, health_service
 from app.services.fail2ban_metadata_service import default_fail2ban_metadata_service
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 
 @dataclass
@@ -93,7 +93,6 @@ class ApplicationContext:
     runtime_settings: Settings | None
     runtime_state: RuntimeState
     session_cache: SessionCache | None
-    login_rate_limiter: RateLimiter
     global_rate_limiter: GlobalRateLimiter
 
 
@@ -120,10 +119,6 @@ def _build_app_context(request: Request) -> ApplicationContext:
     if session_cache is None:
         session_cache = NoOpSessionCache()
 
-    login_rate_limiter: RateLimiter = getattr(state, "login_rate_limiter", None)
-    if login_rate_limiter is None:
-        login_rate_limiter = RateLimiter()
-
     global_rate_limiter: GlobalRateLimiter = getattr(state, "global_rate_limiter", None)
     if global_rate_limiter is None:
         global_rate_limiter = GlobalRateLimiter()
@@ -138,7 +133,6 @@ def _build_app_context(request: Request) -> ApplicationContext:
         runtime_settings=getattr(state, "runtime_settings", None),
         runtime_state=state.runtime_state,
         session_cache=session_cache,
-        login_rate_limiter=login_rate_limiter,
         global_rate_limiter=global_rate_limiter,
     )
 
@@ -264,13 +258,6 @@ async def get_session_cache(app_context: Annotated[ApplicationContext, Depends(g
     return app_context.session_cache
 
 
-async def get_login_rate_limiter(
-    app_context: Annotated[ApplicationContext, Depends(get_app_context)],
-) -> RateLimiter:
-    """Provide the login endpoint rate limiter from application context."""
-    return app_context.login_rate_limiter
-
-
 async def get_global_rate_limiter(
     app_context: Annotated[ApplicationContext, Depends(get_app_context)],
 ) -> GlobalRateLimiter:
@@ -730,7 +717,6 @@ Fail2BanDbRepositoryDep = Annotated[Fail2BanDbRepository, Depends(get_fail2ban_d
 AppStateDep = Annotated[ApplicationContext, Depends(get_app_state)]
 AppDep = Annotated[FastAPI, Depends(get_app)]
 AuthDep = Annotated[Session, Depends(require_auth)]
-LoginRateLimiterDep = Annotated[RateLimiter, Depends(get_login_rate_limiter)]
 GlobalRateLimiterDep = Annotated[GlobalRateLimiter, Depends(get_global_rate_limiter)]
 Fail2BanMetadataServiceDep = Annotated[Fail2BanMetadataService, Depends(get_fail2ban_metadata_service)]