feat(session): persist model tier overrides per session

Store per-session config in SQLite and route /model and /reset through command fast-paths so channel sessions keep independent model selection across reconnects and restarts.

src/automation/heartbeat.ts

@@ -163,7 +163,7 @@ export class HeartbeatMonitor {
         this.notifiedFailure = true;
         const failedChecks = checks.filter((c) => !c.healthy).map((c) => `${c.name}: ${c.message}`);
         await this.notify(`Heartbeat FAILING (${this.consecutiveFailures} consecutive failures):\n${failedChecks.join('\n')}`);
-        
+
         auditLogger?.heartbeatFail({
           checks_failed: failedChecks,
           consecutive_failures: this.consecutiveFailures,
@@ -174,7 +174,7 @@ export class HeartbeatMonitor {
       if (this.notifiedFailure) {
         // Recovery notification
         await this.notify(`Heartbeat RECOVERED after ${this.consecutiveFailures} consecutive failure(s). All checks passing.`);
-        
+
         auditLogger?.heartbeatRecover({
           consecutive_failures_before: this.consecutiveFailures,
         });