feat(ui): form-level onChange with per-input debounce (#2151)

[viniciusdacal]

Summary

• Adds <form onChange={handler}> that fires with all form values (FormValues object) when any child input changes
• Adds debounce={ms} prop on <input>, <textarea>, <select> to control per-input callback timing
• Compiler transforms onChange on <form> to __formOnChange(el, handler) and debounce={N} to data-vertz-debounce="N"

Closes #2151

Public API Changes

Breaking

• onChange on <form> now receives FormValues instead of a DOM Event. Use ref + addEventListener for the raw DOM event.

Additions

• packages/ui/src/dom/form-on-change.ts — __formOnChange runtime helper (compiler target)
• packages/ui/src/jsx-runtime/index.ts — FormHTMLAttributes, InputHTMLAttributes, TextareaHTMLAttributes, SelectHTMLAttributes JSX types
• FormValues type exported from @vertz/ui
• debounce?: number prop on Input/Textarea theme components

Compiler

• native/vertz-compiler-core/src/jsx_transformer.rs — debounce → data-vertz-debounce rename on form elements, onChange on <form> → __formOnChange
• native/vertz-compiler-core/src/import_injection.rs — __formOnChange auto-import

Phases

1. Runtime helper — __formOnChange with microtask batching, per-input debounce via data-vertz-debounce, disposal scope cleanup (18 tests)
2. Compiler transforms — Rust transforms for debounce prop rename and form onChange routing (12 new compiler tests, 81 total)
3. JSX types + theme — Element-specific attribute interfaces, theme component prop forwarding (type-level tests + 4 component tests)
4. Integration + docs — E2E acceptance test (6 scenarios), forms guide update, changeset

Review Findings

Adversarial review found 1 blocker (flush-after-disposal race condition) — fixed by adding disposed flag in flush(). 6 should-fix items addressed (NaN guard, test coverage, comments).

Test plan

• 18 unit tests for __formOnChange runtime helper pass
• 6 E2E acceptance tests (search/filter, rapid typing, mixed interaction, form.reset, cleanup, type safety)
• 81 compiler JSX transform tests pass (12 new, 69 existing)
• Type-level tests verify FormValues handler and debounce: number
• Rust quality gates: cargo test, clippy clean, fmt clean
• TypeScript typecheck clean for packages/ui

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