feat(cua-driver): expose post-action window rebind targets

[f-trycua]

Summary

• add a closed, platform-neutral window_change action-result record with newly discovered native window ids, pids, app names, titles, and foreground-change state
• recommend rebind after any macOS pointer, keyboard, value, or scroll action discovers a new interaction surface, including an exact target when only one window appeared
• preserve the existing read-only window diff and wildcard focus suppression; rediscovery never activates or raises the new surface
• regenerate the portable manifest and Python/TypeScript UniFFI bindings, and document rebind-before-pixel/page/foreground ownership

Why

The macOS detector already observed popups and new windows after native actions, but #2713 narrowed successful actions to the shared ActionResult and retained those target identifiers only in diagnostic prose. Callers therefore remained anchored to a parent window that a modal or popup could block. This change projects the decision-critical topology facts through the same closed contract for every wrapped native action rather than special-casing browser tools.

Malformed producer topology fails closed at the canonical adapter. When multiple windows appear, the result retains every candidate and recommends rebind without guessing an exact target.

Validation

• cargo test --release -p cua-driver-contract -j 1 (26 unit tests + generator test)
• cargo test --release -p cua-driver-core action_record::tests --lib -j 1 (20 passed)
• cargo test --release -p platform-macos window_change_detector::tests --lib -j 1 (10 passed)
• node scripts/generate-uniffi-bindings.mjs --check
• npm run typecheck
• python3 -m py_compile src/cua_driver/__init__.py src/cua_driver/_native_contract.py
• cargo fmt --all -- --check
• git diff --check

Scope

Addresses the structured post-action rediscovery and focus-preservation portion of #2238. The separate privacy-sensitive, request-scoped desktop-frame fallback proposed there is not included in this draft; ambiguous structured results remain recoverable through list_windows without widening capture scope.

Relates to #2238.

[injaneity]

closing as superseded by #3373