feat(observability): add structured audit log channel for API and webhook events

Introduce a dedicated `audit` log channel (daily rotation, configurable retention via
LOG_AUDIT_DAYS) and a small `auditLog()` / `auditLogWebhookFailure()` helper used to
record state-changing API operations and webhook events.

Instrumented:

- API mutation endpoints (create / update / delete / start / stop / restart) across
  applications, services, databases (incl. backups, env vars, storage), servers,
  projects + environments, scheduled tasks, private keys, GitHub apps, cloud provider
  tokens, Hetzner server provisioning, instance enable/disable.
- Webhook signature verification outcomes for GitHub, GitLab, Bitbucket, Gitea and
  Stripe, plus the Sentinel push endpoint.
- Authentication and authorization outcomes via the global exception handler and
  the `ApiAbility` middleware (unauthenticated, ability-denied, policy-denied).

The helper is wrapped in try/catch so logging failures never affect the request
path. Successful operations log at `info`; suspicious/denied requests log at
`warning`. Operators wanting a failures-only feed can set `LOG_AUDIT_LEVEL=warning`.

Includes a feature test suite covering the helper, the webhook providers and the
new auth/authorization log paths.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

routes/api.php

@@ -215,6 +215,8 @@ Route::group([
     Route::post('/sentinel/push', function () {
         $token = request()->header('Authorization');
         if (! $token) {
+            auditLogWebhookFailure('sentinel', 'token_missing');
+
             return response()->json(['message' => 'Unauthorized'], 401);
         }
         $naked_token = str_replace('Bearer ', '', $token);
@@ -222,26 +224,49 @@ Route::group([
             $decrypted = decrypt($naked_token);
             $decrypted_token = json_decode($decrypted, true);
         } catch (Exception $e) {
+            auditLogWebhookFailure('sentinel', 'decrypt_failed');
+
             return response()->json(['message' => 'Invalid token'], 401);
         }
         $server_uuid = data_get($decrypted_token, 'server_uuid');
         if (! $server_uuid) {
+            auditLogWebhookFailure('sentinel', 'invalid_token_payload');
+
             return response()->json(['message' => 'Invalid token'], 401);
         }
         $server = Server::where('uuid', $server_uuid)->first();
         if (! $server) {
+            auditLogWebhookFailure('sentinel', 'server_not_found', [
+                'server_uuid' => $server_uuid,
+            ]);
+
             return response()->json(['message' => 'Server not found'], 404);
         }
 
         if (isCloud() && data_get($server->team->subscription, 'stripe_invoice_paid', false) === false && $server->team->id !== 0) {
+            auditLogWebhookFailure('sentinel', 'subscription_unpaid', [
+                'server_uuid' => $server->uuid,
+                'team_id' => $server->team_id,
+            ]);
+
             return response()->json(['message' => 'Unauthorized'], 401);
         }
 
         if ($server->isFunctional() === false) {
+            auditLogWebhookFailure('sentinel', 'server_not_functional', [
+                'server_uuid' => $server->uuid,
+                'team_id' => $server->team_id,
+            ]);
+
             return response()->json(['message' => 'Server is not functional'], 401);
         }
 
         if ($server->settings->sentinel_token !== $naked_token) {
+            auditLogWebhookFailure('sentinel', 'token_mismatch', [
+                'server_uuid' => $server->uuid,
+                'team_id' => $server->team_id,
+            ]);
+
             return response()->json(['message' => 'Unauthorized'], 401);
         }
         $data = request()->all();
@@ -249,6 +274,11 @@ Route::group([
         // \App\Jobs\ServerCheckNewJob::dispatch($server, $data);
         PushServerUpdateJob::dispatch($server, $data);
 
+        auditLog('sentinel.metrics_pushed', [
+            'server_uuid' => $server->uuid,
+            'team_id' => $server->team_id,
+        ]);
+
         return response()->json(['message' => 'ok'], 200);
     });
 });