feat: capture Windows UIA action evidence

[abrichr]

Summary

• attach a versioned, JSON-safe Windows UIA fingerprint to native mouse-down actions in the existing recording database
• preserve structural evidence through CaptureSession processing and expose it on Action
• add an explicit Recorder toggle and the Windows-only pywinauto runtime dependency
• keep RDP/Citrix recordings pixel-only and reject legacy element-state blobs as trusted structural evidence

Verification

• ruff check openadapt_capture tests/test_structural_observation.py
• 329 passed, 7 skipped with browser-bridge socket tests excluded in the sandbox
• 83 passed across the new schema, input conversion, high-level API, and processing suites
• full localhost browser-bridge run was stopped after an existing test wait; the new UIA path was not involved

[abrichr]

Closing as superseded by #45, which implements the same capture-side contract with the reviewed pywinauto 0.6.9 API, thread-local COM lifecycle, keyboard focus observation, candidate cardinality, additive persistence migration, package verification, and a real Windows smoke. No changes from this branch should be merged.