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/build.sh

@@ -0,0 +1,41 @@
+#!/bin/sh
+set -e
+cd "$(dirname "$0")"
+
+# Install esbuild if not present
+if ! command -v esbuild >/dev/null 2>&1; then
+  if command -v npx >/dev/null 2>&1; then
+    NPX="npx"
+  else
+    echo "esbuild not found. Install it: npm install -g esbuild"
+    exit 1
+  fi
+else
+  NPX=""
+fi
+
+mkdir -p dist
+
+# Build JS bundle
+${NPX:+$NPX} esbuild src/app.jsx \
+  --bundle \
+  --minify \
+  --jsx-factory=h \
+  --jsx-fragment=Fragment \
+  --define:process.env.NODE_ENV=\"production\" \
+  --external:preact \
+  --outfile=dist/app.js \
+  2>/dev/null || \
+${NPX:+$NPX} esbuild src/app.jsx \
+  --bundle \
+  --minify \
+  --jsx-factory=h \
+  --jsx-fragment=Fragment \
+  --define:process.env.NODE_ENV=\"production\" \
+  --outfile=dist/app.js
+
+# Copy static files
+cp src/index.html dist/index.html
+cp src/style.css dist/style.css
+
+echo "Build complete: web/dist/"