feat(listener): add scheduled database cleanup job for expired temporary records

[najeebullahii]

Closes #845.

Changes:

• New scheduled DatabaseCleanupJob (new service file, registered via the existing WorkerManager with graceful shutdown) purging expired temporary data in bounded 1,000-row batched transactions: idempotency keys past expires_at or status EXPIRED, aged processed_events, aged dead-letter and execution-log rows, elapsed rate_limit_events windows, and DEACTIVATED backpressure records.
• Configurable: CLEANUP_ENABLED (default true), CLEANUP_INTERVAL_MS (default 3600000, min 60000), CLEANUP_RETENTION_DAYS (default 30, min 1) validated through the existing config schema; pre-existing per-table retention env vars remain optional overrides; listener/.env.example updated.
• Active records never removed: future-dated PROCESSED idempotency keys, execution-log rows tied to PENDING/PROCESSING notifications, ACTIVATED backpressure records, in-window rate-limit events; live cursors, templates and immutable template-audit history explicitly skipped with logged reasons.
• Ownership boundaries preserved: ArchiveService remains sole owner of scheduled-notification archival and age-based, status-agnostic archive purging (which covers EXPIRED rows from in-flight feat(listener): expire scheduled notifications past a configured deadline #893 once merged); NotificationMetricsRunner owns metrics snapshots. The job logs delegated/skipped owners instead of running competing purges.
• Failure isolation: a per-table failure logs, preserves partial deleted counts, skips that table, and the run continues; per-run log carries a correlation id, per-table counts, skipped/failed tables, retention, interval and duration.
• Tests: 7/7 seeded-SQLite job suite (survival/deletion matrix, batching, failure isolation, shutdown timer cleanliness, enabled/disabled modes); config suite 46/46; archive age/status-agnostic purge assertion. Operator docs section added to NOTIFICATION_LIFECYCLE.md.

Testing: focused suites green (53/53); Prettier and git diff --check clean; no migration added; no package/lockfile changes.

Pre-existing baseline (verified against a stashed clean tree, untouched by this PR): six failures in legacy cleanup/archive tests (two EventRegistry malformed-SCVal fixtures, one legacy timer-call count, three archive API response-shape assertions); full npm test red on main (~55 failing suites: request-id.ts syntax error, Stellar XDR test setup, config secret validation); npm run lint fails on index.ts/request-id.ts/security-headers.ts/discord-notification.ts — index.ts contains a pre-existing malformed startup block which this PR wires around minimally without rewriting; lockfile out of sync with package.json (this PR modifies neither).

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