Replace textual-serve with direct xterm.js 6.0 bundle

- Add package.json with @xterm/xterm 6.0 and all addons
- Create terminal.ts client with WebSocket protocol support
- Bundle with Bun (bun run build -> terminal.js)
- Remove textual-serve dependency from pyproject.toml
- Remove canvas monkey-patch workaround (no longer needed)
- Add scrollback support (configurable via data-scrollback)
- Update static file routing to serve from /static/
- Add Makefile targets: bundle, bundle-watch, bundle-clean
- Update tests for new static path structure

Benefits:
- Full control over xterm.js configuration
- Scrollback history now works (default 1000 lines)
- Custom font family without workarounds
- Smaller footprint (no unused Roboto Mono fonts)
- Latest xterm.js 6.0 features available

package.json

@@ -0,0 +1,21 @@
+{
+  "name": "textual-webterm-frontend",
+  "private": true,
+  "type": "module",
+  "dependencies": {
+    "@xterm/xterm": "^6.0.0",
+    "@xterm/addon-fit": "^0.10.0",
+    "@xterm/addon-webgl": "^0.18.0",
+    "@xterm/addon-canvas": "^0.7.0",
+    "@xterm/addon-unicode11": "^0.8.0",
+    "@xterm/addon-web-links": "^0.11.0",
+    "@xterm/addon-clipboard": "^0.2.0"
+  },
+  "devDependencies": {
+    "typescript": "^5.7.0"
+  },
+  "scripts": {
+    "build": "bun build src/textual_webterm/static/js/terminal.ts --outfile=src/textual_webterm/static/js/terminal.js --minify --target=browser",
+    "watch": "bun build src/textual_webterm/static/js/terminal.ts --outfile=src/textual_webterm/static/js/terminal.js --watch --target=browser"
+  }
+}