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.

.ai/rules/index.md

@@ -0,0 +1,8 @@
+# Project Rules Index
+
+Before planning or editing, find the row whose globs match the file's path and read that rule file.
+
+| Applies to | Rule file |
+| --- | --- |
+| app-modules/shared/src/Bnfexpress/** | .ai/rules/bnfexpress.md |
+| app-modules/*/src/Filament/Pages/** | .ai/rules/pages.md |