Fix AbstractCombobox.onInput() never firing on native input events

[fpigeonjr]

Description

AbstractCombobox (src/ui-kit/experimental/aria/abstract-combobox/abstract-combobox.ts) declares a public onInput(callback, context) method and registers "input" as a valid event name in _initEventDispatcher, but nothing in the class ever dispatched that event — the native input DOM listener in _setupInputEvents only dispatched "search". Any consumer calling combobox.onInput(cb, ctx) registered a callback that was never invoked.

Fixed by dispatching "input" alongside "search" from the same native input listener, so onInput callbacks now fire without changing existing "search" behavior (which sam-picker's onSearch output and its spec depend on).

Added a regression spec (abstract-combobox.spec.ts) mirroring the existing onSearch coverage, confirming onInput callbacks are invoked when the input fires a native input event.

A Playwright/e2e test was intentionally not added — this is a pure event-wiring bug (jsdom's synthetic input dispatch behaves identically to a real browser here), not a CSS-cascade or real-pointer hit-testing issue, so per AGENTS.md's Vitest/Playwright boundary guidance a Vitest spec is sufficient to catch and pin this regression.

Motivation and Context

Closes #659

Type of Change (Select One and Apply Label)

• Bug fix (non-breaking change which fixes an issue) → Apply bugfix label
• New feature (non-breaking change which adds functionality) → Apply enhancement label
• Breaking change (fix or feature that would cause existing functionality to change) → Apply breaking label
• Documentation / configuration update → Apply maintenance label

How to Test

1. npm ci && npm ci --prefix test-app
2. cd test-app && npx vitest run --config vitest.config.mts abstract-combobox — confirm the new "dispatches an input event whenever the input fires a native input event" spec passes, alongside the existing onSearch spec.
3. npm --prefix test-app test — confirm the full suite (151 files / 1378 tests) still passes.

Expected result: onInput(cb, ctx) callbacks registered on AbstractCombobox fire when the underlying input fires a native input event; onSearch continues to fire as before.

Screenshots (if appropriate)

N/A — backend/logic change only, no UI changes.

Checklist

• Branch name follows convention (e.g. gh-<number>-<slug>)
• PR title starts with a verb in the imperative mood
• I have self-reviewed my own code
• format:check passes (npm run format:check)
• lint passes (npm run lint)
• build passes (cd test-app && npm run build)
• Tests pass and coverage is reported (cd test-app && npm test)
• If this change requires a documentation update, I have updated it accordingly
• If there are dependent changes, they have been merged and published in downstream modules

Note on coverage gate: npm run coverage:check currently fails on this branch, but this failure pre-exists on master (verified against a clean clone at db5cc25b, the current master HEAD, and confirmed by the two most recent master CI runs both failing on the same gate) — unrelated to this change. This PR's coverage is measured slightly higher than master's (88.58% vs 88.57% statements) due to the added spec.

[Copilot]

Pull request overview

Fixes AbstractCombobox.onInput() so registered callbacks receive native input events.

Changes:

• Dispatches "input" alongside existing "search" events.
• Adds regression coverage for onInput().

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
abstract-combobox.ts	Dispatches registered input callbacks.
abstract-combobox.spec.ts	Verifies native input event handling.

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