feat: AI provider testing page + multi-provider support + UX design spec

- Add AI Provider Testing page (/admin/ai-test) with Tags and Embeddings tests
- Add new AI providers: CustomOpenAI, DeepSeek, OpenRouter
- Add API routes for AI config, models listing, and testing endpoints
- Add UX Design Specification document for Phase 1 MVP AI
- Add PRD Phase 1 MVP AI planning document
- Update admin settings and sidebar navigation
- Fix AI factory for multi-provider support

.claude/settings.local.json

@@ -28,7 +28,8 @@
       "Bash(curl:*)",
       "Bash(python:*)",
       "Bash(npm test:*)",
-      "Skill(bmad:bmm:agents:ux-designer)"
+      "Skill(bmad:bmm:agents:ux-designer)",
+      "Skill(bmad:bmm:workflows:create-prd)"
     ]
   }
 }