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/tasks/blocklist_import.py

@@ -21,7 +21,7 @@ from __future__ import annotations
 import uuid
 from typing import TYPE_CHECKING, Any
 
-import structlog
+from app.utils.logging_compat import get_logger
 
 from app.services import ban_service, blocklist_service
 from app.tasks.db import task_db
@@ -35,7 +35,7 @@ if TYPE_CHECKING:
 
     from app.config import Settings
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 #: Stable APScheduler job id so the job can be replaced without duplicates.
 JOB_ID: str = "blocklist_import"

backend/app/tasks/geo_cache_cleanup.py

@@ -18,7 +18,7 @@ import uuid
 from datetime import UTC, datetime, timedelta
 from typing import TYPE_CHECKING
 
-import structlog
+from app.utils.logging_compat import get_logger
 
 from app.repositories import geo_cache_repo
 from app.tasks.db import task_db
@@ -31,7 +31,7 @@ if TYPE_CHECKING:
 
     from app.config import Settings
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 #: How long to retain geo cache entries (days). Configurable tuning constant.
 GEO_CACHE_RETENTION_DAYS: int = 90

backend/app/tasks/geo_cache_flush.py

@@ -17,7 +17,7 @@ from __future__ import annotations
 import uuid
 from typing import TYPE_CHECKING
 
-import structlog
+from app.utils.logging_compat import get_logger
 
 from app.tasks.db import task_db
 from app.tasks.timeout_utils import run_with_timeout
@@ -30,7 +30,7 @@ if TYPE_CHECKING:
     from app.config import Settings
     from app.services.geo_cache import GeoCache
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 #: How often the flush job fires (seconds).  Configurable tuning constant.
 GEO_FLUSH_INTERVAL: int = 60

backend/app/tasks/geo_re_resolve.py

@@ -23,7 +23,7 @@ from __future__ import annotations
 import uuid
 from typing import TYPE_CHECKING
 
-import structlog
+from app.utils.logging_compat import get_logger
 
 from app.tasks.db import task_db
 from app.tasks.timeout_utils import run_with_timeout
@@ -37,7 +37,7 @@ if TYPE_CHECKING:
     from app.config import Settings
     from app.services.geo_cache import GeoCache
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 #: How often the re-resolve job fires (seconds).  10 minutes.
 GEO_RE_RESOLVE_INTERVAL: int = 600

backend/app/tasks/health_check.py

@@ -26,7 +26,7 @@ import uuid
 from contextvars import copy_context
 from typing import TYPE_CHECKING
 
-import structlog
+from app.utils.logging_compat import get_logger
 
 from app.models.server import ServerStatus
 from app.services import health_service
@@ -44,7 +44,7 @@ if TYPE_CHECKING:  # pragma: no cover
 
     from app.config import Settings
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 
 #: How often the probe fires (seconds).

backend/app/tasks/history_sync.py

@@ -13,7 +13,7 @@ import datetime
 import uuid
 from typing import TYPE_CHECKING
 
-import structlog
+from app.utils.logging_compat import get_logger
 
 from app.services import history_service
 from app.tasks.db import task_db
@@ -26,7 +26,7 @@ if TYPE_CHECKING:
 
     from app.config import Settings
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 #: Stable APScheduler job id.
 JOB_ID: str = "history_sync"

backend/app/tasks/rate_limiter_cleanup.py

@@ -18,7 +18,7 @@ from __future__ import annotations
 import uuid
 from typing import TYPE_CHECKING
 
-import structlog
+from app.utils.logging_compat import get_logger
 
 from app.tasks.timeout_utils import run_with_timeout
 from app.utils.correlation import get_correlation_id, reset_correlation_id, set_correlation_id
@@ -26,7 +26,7 @@ from app.utils.correlation import get_correlation_id, reset_correlation_id, set_
 if TYPE_CHECKING:
     from fastapi import FastAPI
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 #: How often the cleanup job fires (seconds). Chosen to balance memory
 #: management against CPU overhead. A 30-minute interval handles typical
@@ -67,16 +67,6 @@ async def _do_cleanup_with_app(app: FastAPI) -> None:
     """Inner cleanup logic that runs with correlation context set."""
 
     async def _do_cleanup() -> None:
-        login_limiter = getattr(app.state, "login_rate_limiter", None)
-        if login_limiter is None:
-            log.warning(
-                "rate_limiter_cleanup_skipped",
-                correlation_id=get_correlation_id(),
-                reason="login_rate_limiter not found on app.state",
-            )
-        else:
-            login_limiter.cleanup_expired()
-
         global_limiter = getattr(app.state, "global_rate_limiter", None)
         if global_limiter is None:
             log.warning(

backend/app/tasks/scheduler_lock_heartbeat.py

@@ -17,7 +17,7 @@ from __future__ import annotations
 import uuid
 from typing import TYPE_CHECKING
 
-import structlog
+from app.utils.logging_compat import get_logger
 
 from app.tasks.db import task_db
 from app.tasks.timeout_utils import run_with_timeout
@@ -30,7 +30,7 @@ if TYPE_CHECKING:
 
     from app.config import Settings
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 #: How often the heartbeat job fires (seconds). Must be significantly less than
 #: the lock TTL to allow multiple missed heartbeats before lock expiry.

backend/app/tasks/session_cleanup.py

@@ -16,7 +16,7 @@ from __future__ import annotations
 import uuid
 from typing import TYPE_CHECKING
 
-import structlog
+from app.utils.logging_compat import get_logger
 
 from app.repositories import session_repo
 from app.tasks.db import task_db
@@ -30,7 +30,7 @@ if TYPE_CHECKING:
 
     from app.config import Settings
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 #: How often the cleanup job fires (seconds).  Configurable tuning constant.
 SESSION_CLEANUP_INTERVAL: int = 6 * 60 * 60  # 6 hours

backend/app/tasks/timeout_utils.py

@@ -12,9 +12,9 @@ import time
 from collections.abc import Awaitable
 from typing import TypeVar
 
-import structlog
+from app.utils.logging_compat import get_logger
 
-log: structlog.stdlib.BoundLogger = structlog.get_logger()
+log = get_logger(__name__)
 
 T = TypeVar("T")