Add embedded web chat client with C2S HTTP API

- New DB schema: users, channel_members, messages tables (migration 003)
- Full C2S HTTP API: register, channels, messages, DMs, polling
- Preact SPA embedded via embed.FS, served at GET /
- IRC-style UI: tab bar, channel messages, user list, DM tabs, /commands
- Dark theme, responsive, esbuild-bundled (~19KB)
- Polling-based message delivery (1.5s interval)
- Commands: /join, /part, /msg, /nick

web/package.json

@@ -0,0 +1,18 @@
+{
+  "name": "web",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "devDependencies": {
+    "esbuild": "^0.27.3"
+  },
+  "dependencies": {
+    "preact": "^10.28.3"
+  }
+}