feat(ui): add semantic and text input ABI - #18

Summary

• extend eight-byte input records with bounded UTF-8 text, IME, focus, and wheel events
• add a bounded host_ui_semantics_submit output carrying a validated semantic control tree
• expose semantic output and extended input through native, browser interpreter, and translated browser runtimes
• document the ABI and ship synchronized browser assets

Contract

UI automation consumes semantic roles, names, values, actions, focus, and surface-relative bounds, but every interaction returns through actual pointer, keyboard, text, or IME input records. It cannot invoke guest functions directly.

Verification

• cargo test -p pvm-runtime --locked — 33 passed
• npm test — 10 browser tests passed and embedded assets matched
• cargo fmt --all -- --check
• git diff --check