feat: add automatic event cleanup based on retention setting

Hourly background task deletes events older than configured
retention period (default 90 days). Reads event_retention_days
from settings table. Includes 2 tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_cleanup.py

@@ -0,0 +1,65 @@
+"""Tests for event retention cleanup."""
+
+import sqlite3
+
+from database import init_db, set_db_path
+
+
+def test_cleanup_deletes_old_events(db_path):
+    """Old events beyond retention should be deleted."""
+    set_db_path(db_path)
+    init_db()
+    conn = sqlite3.connect(db_path)
+    conn.row_factory = sqlite3.Row
+
+    # Insert an old event (100 days ago)
+    conn.execute(
+        """INSERT INTO events (frigate_event_id, camera, label, score, match_status, created_at)
+           VALUES ('old-1', 'cam', 'person', 0.9, 'unknown', datetime('now', '-100 days'))"""
+    )
+    # Insert a recent event
+    conn.execute(
+        """INSERT INTO events (frigate_event_id, camera, label, score, match_status)
+           VALUES ('new-1', 'cam', 'person', 0.9, 'unknown')"""
+    )
+    conn.commit()
+
+    # Simulate cleanup with 90-day retention
+    result = conn.execute(
+        "DELETE FROM events WHERE created_at < datetime('now', '-90 days')"
+    )
+    conn.commit()
+    assert result.rowcount == 1
+
+    remaining = conn.execute("SELECT COUNT(*) as c FROM events").fetchone()["c"]
+    assert remaining == 1
+    conn.close()
+
+
+def test_cleanup_preserves_recent_events(db_path):
+    """Events within retention period should not be deleted."""
+    set_db_path(db_path)
+    init_db()
+    conn = sqlite3.connect(db_path)
+    conn.row_factory = sqlite3.Row
+
+    # Insert events from 30 and 60 days ago
+    conn.execute(
+        """INSERT INTO events (frigate_event_id, camera, label, score, match_status, created_at)
+           VALUES ('mid-1', 'cam', 'person', 0.9, 'unknown', datetime('now', '-30 days'))"""
+    )
+    conn.execute(
+        """INSERT INTO events (frigate_event_id, camera, label, score, match_status, created_at)
+           VALUES ('mid-2', 'cam', 'car', 0.8, 'known', datetime('now', '-60 days'))"""
+    )
+    conn.commit()
+
+    result = conn.execute(
+        "DELETE FROM events WHERE created_at < datetime('now', '-90 days')"
+    )
+    conn.commit()
+    assert result.rowcount == 0
+
+    remaining = conn.execute("SELECT COUNT(*) as c FROM events").fetchone()["c"]
+    assert remaining == 2
+    conn.close()