perf,feat(events),ops: third optimization pass

Overview cold start:
- InstanceResourceService persists every live fetch into status_snapshots
  (category 'resources') and serves a snapshot younger than 2 minutes
  before calling upstream, so the first fleet overview after a restart
  costs zero device requests; instance deletion cleans up via FK cascade

Bounded retention for the four fastest-growing tables (15-minute sweep):
- connection_logs: one row per probe per beat had no automatic cleanup
- audit_events: new pruneBefore (90d)
- operation_preparations: every prepare/retry attempt inserted a row,
  terminal rows now expire after 7 days
- notification_queue: terminal rows pruned after 30 days

SSE events now cover instance lifecycle:
- create/update emit instance envelopes from the routes; the two-phase
  delete emits a job envelope on every terminal transition plus an
  instance envelope when the node actually disappears, so fleet and
  instance views invalidate in real time

Linux ops:
- 'install.sh unit' writes systemd user units for API and gateway with
  Restart=on-failure, 0600 secret injection, and
  MULTI_SIMADMIN_SYSTEMD_UNIT wired so console self-update restarts via
  systemctl -- closing the self-update loop on Linux

apps/api/src/application/operations/secure-operation-execution.ts

@@ -449,6 +449,24 @@ export class SecureOperationExecution {
     return this.job(ids.job);
   }
 
+  /**
+   * Retention for consumed/expired/invalidated preparations. Every prepare
+   * (manual or a scheduled retry attempt) inserts a row, so without this the
+   * table grows one row per attempt forever.
+   */
+  pruneTerminalPreparations(olderThanMs: number): number {
+    if (!Number.isSafeInteger(olderThanMs) || olderThanMs < 0)
+      throw new RangeError('olderThanMs must be a non-negative integer');
+    const cutoff = new Date(this.clock().getTime() - olderThanMs).toISOString();
+    return Number(
+      this.options.db
+        .prepare(
+          "DELETE FROM operation_preparations WHERE status IN ('consumed','expired','invalidated') AND updated_at <= ?",
+        )
+        .run(cutoff).changes,
+    );
+  }
+
   reconcileInterruptedJobs(): number {
     const now = this.clock().toISOString();
     return this.options.db.transaction(() => {