Add strict browser wrappers for window timers and navigator share

[sbsoftware-agent]

Summary

Adds typed browser context wrappers for window timers and navigator.share so strict-mode snippets can use real browser globals without _literal_js.

Changes

• Added JS::Context::Window with:
• setTimeout(callback, delay) returning a typed JS::Context::TimerHandle
• clearTimeout(handle) accepting that typed handle
• Added JS::Context::Navigator#share with typed named args:
• required text
• optional title and url
• Added JS::Context::ShareData to emit the share payload object literal.
• Exposed new strict entrypoints via JS::Context::Browser:
• window
• navigator
• Added specs covering:
• strict-mode timer snippet emission (window.setTimeout + window.clearTimeout)
• strict-mode share snippet emission (navigator.share)
• typed wrapper return behavior and to_js_ref output
• Updated README browser-wrapper docs to include the new APIs and example usage.

Testing

• CRYSTAL_CACHE_DIR=/tmp/.crystal-cache-js crystal spec
• Result: 53 examples, 0 failures, 0 errors, 0 pending