Move / endpoint to /topics and add version endpoint

- Move GET / to GET /topics for listing topics
- Add new GET / endpoint that returns server version (git commit hash)
- Update build.js to inject git commit hash as RONDEVU_VERSION
- Update API documentation

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

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

build.js

@@ -1,5 +1,14 @@
 // Build script using esbuild
 const esbuild = require('esbuild');
+const { execSync } = require('child_process');
+
+// Get git commit hash
+let version = 'unknown';
+try {
+  version = execSync('git rev-parse --short HEAD', { encoding: 'utf8' }).trim();
+} catch (err) {
+  console.warn('Could not get git commit hash, using "unknown"');
+}
 
 esbuild.build({
   entryPoints: ['src/index.ts'],
@@ -14,4 +23,7 @@ esbuild.build({
     'hono'
   ],
   sourcemap: true,
+  define: {
+    'process.env.RONDEVU_VERSION': JSON.stringify(version)
+  }
 }).catch(() => process.exit(1));