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/lux.toml

@@ -0,0 +1,8 @@
+[project]
+name = "stdlib"
+version = "0.1.0"
+description = "Lux Standard Library - Core types and effects for browser development"
+license = "MIT"
+
+[dependencies]
+# No dependencies - this is the core library