feat: add V2 service publishing and username claiming APIs

- Add POST /services endpoint for publishing services with username verification
- Add DELETE /services/:serviceId endpoint for unpublishing services
- Add GET /services/:serviceFqn endpoint for service discovery
- Add POST /usernames/claim endpoint with Ed25519 signature verification
- Add POST /usernames/renew endpoint for extending username TTL
- Add GET /usernames/:username endpoint for checking username availability
- Add username expiry tracking and cleanup (365-day default TTL)
- Add service-to-offer relationship tracking
- Add signature verification for username operations
- Update storage schema for usernames and services tables
- Add comprehensive README documentation for V2 APIs
- Update version to 0.8.0

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

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

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@xtr-dev/rondevu-server",
-  "version": "0.1.5",
-  "description": "Topic-based peer discovery and signaling server for distributed P2P applications",
+  "version": "2.0.0",
+  "description": "DNS-like WebRTC signaling server with username claiming and service discovery",
   "main": "dist/index.js",
   "scripts": {
     "build": "node build.js",
@@ -21,6 +21,7 @@
   },
   "dependencies": {
     "@hono/node-server": "^1.19.6",
+    "@noble/ed25519": "^3.0.0",
     "better-sqlite3": "^12.4.1",
     "hono": "^4.10.4"
   }