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/shared/tests/Unit/BnfexpressSignatureTest.php

@@ -0,0 +1,46 @@
+<?php
+
+use Modules\Shared\Bnfexpress\Support\BnfexpressSignature;
+
+test('headers computes the hex HMAC-SHA256 over METHOD\PATH\TIMESTAMP\RAW_BODY joined by newlines', function () {
+    $headers = BnfexpressSignature::headers(
+        method: 'post',
+        path: '/admin/faqs',
+        rawBody: '{"content":"hi"}',
+        clientId: 'ev_admin',
+        secret: 'shared-secret',
+        timestamp: 1_700_000_000,
+    );
+
+    $expected = hash_hmac('sha256', "POST\n/admin/faqs\n1700000000\n{\"content\":\"hi\"}", 'shared-secret');
+
+    expect($headers)->toBe([
+        'X-Client-Id' => 'ev_admin',
+        'X-Timestamp' => '1700000000',
+        'X-Signature' => $expected,
+    ]);
+});
+
+test('headers signs an empty raw body for a bodyless request', function () {
+    $headers = BnfexpressSignature::headers(
+        method: 'GET',
+        path: '/admin/faqs/1',
+        rawBody: '',
+        clientId: 'ev_admin',
+        secret: 'shared-secret',
+        timestamp: 1_700_000_000,
+    );
+
+    $expected = hash_hmac('sha256', "GET\n/admin/faqs/1\n1700000000\n", 'shared-secret');
+
+    expect($headers['X-Signature'])->toBe($expected);
+});
+
+test('headers generates a fresh timestamp per call when none is given', function () {
+    $before = time();
+
+    $headers = BnfexpressSignature::headers('GET', '/admin/faqs', '', 'ev_admin', 'secret');
+
+    expect((int) $headers['X-Timestamp'])->toBeGreaterThanOrEqual($before)
+        ->and((int) $headers['X-Timestamp'])->toBeLessThanOrEqual(time());
+});