feat: store warnings and request lines in log_events

The log now has a stored, queryable copy for the diagnostics console:
every WARNING and above plus the request line of every request, kept
for log_retention_days (default 7, no "forever") and pruned hourly by
the new log_gc job.

Rows are built on the logging thread from the same redacted fields as
the stdout line, queued without blocking and written in batches by one
background thread on its own connection. A full queue or a failed write
drops and reports instead of retrying. Flood control keeps 30 of any
one message per minute plus a count of the rest; anonymous request
lines are capped at 60 a minute per client, and the client address is
never stored. Deleting an account deletes its stored events.

Measured on prod first: a YouTube RSS outage wrote 11k warnings in four
hours, one per channel per poll. The poll now writes one warning with
per-reason counts and a few examples, and a failure on our side gets
one traceback per poll instead of one per channel.

backend/app/scheduler.py

@@ -10,7 +10,7 @@ from typing import Callable
 from apscheduler.schedulers.background import BackgroundScheduler
 from sqlalchemy import select
 
-from app import audit, progress, quota
+from app import audit, logsink, progress, quota
 from app.audit import AuditAction
 from app.config import settings
 from app.db import SessionLocal
@@ -72,6 +72,7 @@ JOB_INTERVALS: dict[str, int] = {
     "plex_watch_reconcile": settings.plex_watch_reconcile_interval_min,
     "tmdb_enrich": settings.tmdb_enrich_interval_min,
     "audit_gc": settings.audit_gc_minutes,
+    "log_gc": settings.log_gc_minutes,
 }
 
 # Sane bounds for an admin-set interval (minutes).
@@ -381,6 +382,19 @@ def _audit_gc_job() -> None:
     _job("audit_gc", work)
 
 
+def _log_gc_job() -> None:
+    # Prune log_events rows older than log_retention_days — the limit the privacy policy states, so
+    # this runs hourly rather than daily. Pure DB, no quota.
+    def work(db):
+        from app import sysconfig
+
+        reaped = logsink.gc(db, sysconfig.get_int(db, "log_retention_days"))
+        db.commit()
+        return {"reaped": reaped}
+
+    _job("log_gc", work)
+
+
 # job_id -> wrapper. The single source of truth for which jobs exist and how to run one,
 # shared by start_scheduler (recurring registration) and trigger_job (manual "run now").
 JOB_FUNCS: dict[str, Callable[[], None]] = {
@@ -400,6 +414,7 @@ JOB_FUNCS: dict[str, Callable[[], None]] = {
     "plex_watch_reconcile": _plex_watch_reconcile_job,
     "tmdb_enrich": _tmdb_enrich_job,
     "audit_gc": _audit_gc_job,
+    "log_gc": _log_gc_job,
 }