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>

bootstrap/helpers/audit.php

@@ -0,0 +1,81 @@
+<?php
+
+use Illuminate\Support\Facades\Log;
+
+if (! function_exists('auditLog')) {
+    /**
+     * Write a security-relevant audit entry to the dedicated `audit` log channel.
+     *
+     * Never include secrets (private keys, passwords, tokens, webhook secrets,
+     * signature header values, env-var values) in $context.
+     *
+     * @param  string  $event  Dot-namespaced event name, e.g. `api.private_key.created`.
+     * @param  array<string, mixed>  $context  Identifiers + outcome details.
+     * @param  string  $level  Log level: info | warning | error.
+     */
+    function auditLog(string $event, array $context = [], string $level = 'info'): void
+    {
+        try {
+            $request = app()->bound('request') ? request() : null;
+            $user = auth()->check() ? auth()->user() : null;
+            $token = $user?->currentAccessToken();
+
+            $base = [
+                'event' => $event,
+                'ip' => $request?->ip(),
+                'ua' => substr((string) $request?->userAgent(), 0, 200),
+                'user_id' => $user?->id,
+                'user_email' => $user?->email,
+                'team_id' => $token ? data_get($token, 'team_id') : null,
+                'token_id' => $token?->id ?? null,
+                'token_name' => $token?->name ?? null,
+                'method' => $request?->method(),
+                'path' => $request?->path(),
+            ];
+
+            $payload = array_merge($base, $context);
+
+            Log::channel('audit')->{$level}($event, $payload);
+        } catch (Throwable $e) {
+            // Audit logging must never break the request path.
+            try {
+                Log::warning('auditLog failed: '.$e->getMessage(), ['event' => $event]);
+            } catch (Throwable) {
+            }
+        }
+    }
+}
+
+if (! function_exists('auditLogWebhookFailure')) {
+    /**
+     * Record a webhook signature/auth verification failure to the `audit` channel.
+     */
+    function auditLogWebhookFailure(string $provider, string $reason, array $context = []): void
+    {
+        try {
+            $request = app()->bound('request') ? request() : null;
+
+            $event = "webhook.{$provider}.signature_failed";
+
+            $base = [
+                'event' => $event,
+                'reason' => $reason,
+                'ip' => $request?->ip(),
+                'ua' => substr((string) $request?->userAgent(), 0, 200),
+                'method' => $request?->method(),
+                'path' => $request?->path(),
+                'event_header' => $request?->header('X-GitHub-Event')
+                    ?? $request?->header('X-Gitlab-Event')
+                    ?? $request?->header('X-Gitea-Event')
+                    ?? $request?->header('X-Event-Key'),
+            ];
+
+            Log::channel('audit')->warning($event, array_merge($base, $context));
+        } catch (Throwable $e) {
+            try {
+                Log::warning('auditLogWebhookFailure failed: '.$e->getMessage(), ['provider' => $provider]);
+            } catch (Throwable) {
+            }
+        }
+    }
+}