Add complete BlackRoad OS backend API and wire all apps

- Created FastAPI backend with all endpoints (auth, agents, chat, blockchain, payments)
- Added unified BlackRoad API client (blackroad-api.js) for all frontend apps
- Updated index.html to use new unified API
- Backend includes health checks, JWT auth, and mock AI responses
- Ready for Railway deployment with Procfile and railway.json
- All frontend apps can now share authentication and API calls

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/railway.json

@@ -0,0 +1,13 @@
+{
+  "$schema": "https://railway.app/railway.schema.json",
+  "build": {
+    "builder": "NIXPACKS"
+  },
+  "deploy": {
+    "startCommand": "uvicorn main:app --host 0.0.0.0 --port $PORT",
+    "healthcheckPath": "/health",
+    "healthcheckTimeout": 100,
+    "restartPolicyType": "ON_FAILURE",
+    "restartPolicyMaxRetries": 10
+  }
+}