feat: Implement content-based offer IDs with SHA-256 hashing

- Added hash-id.ts utility for SHA-256 content hashing
- Offer IDs now generated from hash of {sdp, topics} (sorted)
- Removed peerId from hash (inferred from authentication)
- Server generates deterministic IDs for idempotent offer creation
- Updated SQLite and D1 storage implementations
- Removed optional id field from CreateOfferRequest
- Same offer content always produces same ID

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

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

build.js

@@ -0,0 +1,29 @@
+// 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'],
+  bundle: true,
+  platform: 'node',
+  target: 'node20',
+  outfile: 'dist/index.js',
+  format: 'cjs',
+  external: [
+    'better-sqlite3',
+    '@hono/node-server',
+    'hono'
+  ],
+  sourcemap: true,
+  define: {
+    'process.env.RONDEVU_VERSION': JSON.stringify(version)
+  }
+}).catch(() => process.exit(1));