Wake Chromium accessibility trees per PID

[FuJacob]

Summary

Restore Chromium-family Accessibility wake-up in the focus pipeline so Tabby can see usable AX trees in Chrome, Arc, Edge, Brave, and common Electron shells. The change adds a dedicated wake service that tracks wake state per PID, sets AXManualAccessibility on both app and renderer-owned AX elements, and confirms wake success by waiting for AXChildren to become non-empty before treating the process as ready.

Validation

xcodebuild -scheme tabby -destination 'platform=macOS' build
# ** BUILD SUCCEEDED **

xcodebuild -scheme tabby -destination 'platform=macOS' test
# Test run did not complete in this environment: the hosted tabbyTests bundle failed to load because the test bundle Team ID did not match the app process, and the run then terminated inside an unrelated llama Metal teardown assertion.

Linked issues

Fixes #19

Risk / rollout notes

• The wake service intentionally keys readiness by process ID instead of bundle ID because Electron renderer processes can restart underneath the same app shell.
• Renderer wake-up is done with a bounded descendant walk on every tracked Chromium-family bundle instead of brittle version detection. That is slightly more AX work, but materially safer for Electron 28+ webviews.
• This PR restores the primary AX data source. It does not implement the separate key-event prefix fallback from #17.

[FuJacob]

@copilot resolve the merge conflicts in this pull request