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

pyproject.toml

@@ -6,11 +6,14 @@ authors = ["Will McGugan <will@textualize.io>"]
 license = "MIT"
 readme = "README.md"
 packages = [{include = "textual_webterm", from = "src"}]
-include = [{ path = "src/textual_webterm/static/monospace.css" }]
+include = [
+    { path = "src/textual_webterm/static/monospace.css" },
+    { path = "src/textual_webterm/static/css/xterm.css" },
+    { path = "src/textual_webterm/static/js/terminal.js" },
+]
 
 [tool.poetry.dependencies]
 python = "^3.9"
-textual-serve = "^1.1.0"
 aiohttp = "^3.13.0"
 uvloop = { version = "^0.22.0", markers = "sys_platform != 'win32'" }
 click = "^8.1.7"