feat: add Next.js metrics dashboard for real-time visualization

Add a lightweight Next.js dashboard to visualize OpenProxy metrics in real-time. The dashboard provides comprehensive insights into LLM API usage, costs, and performance.

Features:
- Real-time metrics overview (requests, tokens, costs, response times)
- Model breakdown with usage statistics
- Hourly trends visualization with charts
- Recent requests table with detailed information
- Auto-refresh every 30 seconds
- Configurable time ranges (1h, 6h, 24h, 7d)

Technical details:
- Built with Next.js 14 and React 18
- Uses Recharts for data visualization
- Connects directly to PostgreSQL database
- Runs on port 3008 by default
- TypeScript for type safety
- Minimal dependencies for lightweight deployment

The dashboard complements the proxy server by providing a user-friendly interface for monitoring and analyzing LLM API usage patterns.

dashboard/tsconfig.json

@@ -0,0 +1,27 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "lib": ["dom", "dom.iterable", "esnext"],
+    "allowJs": true,
+    "skipLibCheck": true,
+    "strict": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "module": "esnext",
+    "moduleResolution": "bundler",
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "jsx": "preserve",
+    "incremental": true,
+    "plugins": [
+      {
+        "name": "next"
+      }
+    ],
+    "paths": {
+      "@/*": ["./*"]
+    }
+  },
+  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
+  "exclude": ["node_modules"]
+}