Add bnfexpress signed admin client and AI Agent Filament UI

- Modules\Shared\Bnfexpress\BnfexpressAdminClient: HMAC-signed HTTP client
  for bnfexpress's admin API (EV FAQs, agent instructions, chat history),
  with a bnfexpress:smoke-test command and full unit coverage.
- New ai-agent module: Filament pages to manage EV FAQs, publish/roll back
  agent instruction versions, and browse EV chat history + transcripts.
- New manage_ai_agent permission (super_admin/admin).
- Recorded .ai/rules for the client's auth scheme and non-Resource
  Filament page/table testing gotchas.

app-modules/ai-agent/src/AiAgentPlugin.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Modules\AiAgent;
+
+use Filament\Contracts\Plugin;
+use Filament\Panel;
+
+class AiAgentPlugin implements Plugin
+{
+    public function getId(): string
+    {
+        return 'ai-agent';
+    }
+
+    public function register(Panel $panel): void
+    {
+        $panel->discoverPages(
+            in: __DIR__.'/Filament/Pages',
+            for: 'Modules\AiAgent\Filament\Pages',
+        );
+    }
+
+    public function boot(Panel $panel): void {}
+
+    public static function make(): static
+    {
+        return app(static::class);
+    }
+}