test(fence): owner filters in any form, statement writes under any name, core commits by list

The owner-filter check missed an aliased() model, an import alias, .in_() and
filter_by; four live inline filters on aliased VideoState go through owned_by now.
Cross-unit writes are seen under any import name, through sa.update and via
__table__. Core modules may commit only where CORE_COMMITS names the reason;
trim_read and audit.gc flush now and their callers commit. The pin target, the
debug-session header and a link's target fetch through owned_row. The docs
claim what the fence holds, and say what is beyond it.

backend/app/audit.py

@@ -110,10 +110,9 @@ def record(
 
 def gc(db: Session, retention_days: int) -> int:
     """Delete audit rows older than `retention_days`. Returns the number removed. A
-    retention_days <= 0 disables pruning (keep forever)."""
+    retention_days <= 0 disables pruning (keep forever). Flushes; the job commits."""
     if retention_days <= 0:
         return 0
     cutoff = datetime.now(timezone.utc) - timedelta(days=retention_days)
     result = db.execute(delete(AuditLog).where(AuditLog.created_at < cutoff))
-    db.commit()
     return result.rowcount or 0