Replace preset topics with dynamic topic listing from server

Changed discover page to fetch and display real topics from the API:
- Added fetchTopics() to call client.offers.getTopics()
- Display actual topic names and active peer counts
- Added loading, error, and empty states
- Added refresh button to reload topics
- Improved UX with better error handling

Updated to @xtr-dev/rondevu-client@0.7.4

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

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

package-lock.json

@@ -8,7 +8,7 @@
       "name": "rondevu-demo",
       "version": "0.5.0",
       "dependencies": {
-        "@xtr-dev/rondevu-client": "^0.7.3",
+        "@xtr-dev/rondevu-client": "^0.7.4",
         "@zxing/library": "^0.21.3",
         "qrcode": "^1.5.4",
         "react": "^18.2.0",
@@ -1171,9 +1171,9 @@
       }
     },
     "node_modules/@xtr-dev/rondevu-client": {
-      "version": "0.7.3",
-      "resolved": "https://registry.npmjs.org/@xtr-dev/rondevu-client/-/rondevu-client-0.7.3.tgz",
-      "integrity": "sha512-WcKc+q1JOh/v5doX0PaX9pYIJa0ofJHgxUo+xdOIjuBjUQuQW+F1G71NxtzCia2A62VPJdctL5TgADNKYmlIHQ==",
+      "version": "0.7.4",
+      "resolved": "https://registry.npmjs.org/@xtr-dev/rondevu-client/-/rondevu-client-0.7.4.tgz",
+      "integrity": "sha512-MPmw9iSc7LxLduu4TtVrcPvBl/Cuul5sqgOAKUWW7XYXYAObFYUtu9RcbWShR+a6Bwwx7oHadz5I2U8eWsebXQ==",
       "license": "MIT",
       "dependencies": {
         "@xtr-dev/rondevu-client": "^0.5.1"