feat(audit): Add automation component logging

Add audit logging to:
- WebhookHandler: connect/disconnect, receive, not_found, denied, HMAC verified
- HeartbeatMonitor: start/stop, cycle, check, fail, recover
- GmailWatcher: connect/disconnect lifecycle events

All automation events now captured in audit log with proper context

src/automation/heartbeat.ts

@@ -2,6 +2,7 @@ import { statfsSync, accessSync, constants as fsConstants } from 'fs';
 import { request } from 'http';
 import type { HeartbeatConfig, HeartbeatCheck } from '../config/schema.js';
 import type { ChannelAdapter, ChannelStatus, OutboundMessage } from '../channels/types.js';
+import { auditLogger } from '../audit/index.js';
 
 /** Result of a single health check. */
 export interface CheckResult {
@@ -77,6 +78,7 @@ export class HeartbeatMonitor {
 
     const intervalMs = parseInterval(this.deps.config.interval);
     console.log(`HeartbeatMonitor: starting (interval=${this.deps.config.interval}, checks=[${this.deps.config.checks.join(', ')}])`);
+    auditLogger?.systemStart('HeartbeatMonitor', { interval: this.deps.config.interval, checks: this.deps.config.checks });
 
     this.timer = setInterval(() => {
       this.runChecks().catch((err) => {
@@ -96,6 +98,7 @@ export class HeartbeatMonitor {
       clearInterval(this.timer);
       this.timer = undefined;
     }
+    auditLogger?.systemStop('HeartbeatMonitor');
   }
 
   /** Run all configured checks and return the result. */
@@ -136,6 +139,12 @@ export class HeartbeatMonitor {
       }
 
       checks.push(result);
+      auditLogger?.heartbeatCheck({
+        check_name: result.name,
+        healthy: result.healthy,
+        message: result.message,
+        duration_ms: result.durationMs,
+      });
     }
 
     const healthy = checks.every((c) => c.healthy);
@@ -154,16 +163,33 @@ 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,
+          threshold: this.deps.config.failure_threshold,
+        });
       }
     } else {
       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,
+        });
       }
       this.consecutiveFailures = 0;
       this.notifiedFailure = false;
     }
 
+    auditLogger?.heartbeatCycle({
+      interval_ms: parseInterval(this.deps.config.interval),
+      checks: this.deps.config.checks,
+      healthy,
+      consecutive_failures: this.consecutiveFailures,
+    });
+
     return heartbeatResult;
   }