feat: add stdlib and browser examples

- stdlib/html.lux: Type-safe HTML construction
- stdlib/browser.lux: Browser utilities
- examples/web/: Counter app with DOM manipulation
- examples/counter.lux: Simple counter example

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

stdlib/lib.lux

@@ -0,0 +1,8 @@
+// Lux Standard Library
+//
+// This module re-exports the core standard library modules.
+// Import with: import stdlib
+
+// Re-export Html module
+pub import html
+pub import browser