feat: implement usage tracking for AI requests

Adds local token usage tracking for all AI providers. Usage data is
captured during stream processing and stored in a local database.
Includes a new Usage tab in the Providers dashboard to visualize
historical token consumption.

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

package.json

@@ -4,7 +4,7 @@
   "description": "9Router web dashboard",
   "private": true,
   "scripts": {
-    "dev": "next dev",
+    "dev": "next dev --port 3091",
     "build": "next build",
     "start": "next start"
   },