Windows: selected window source records full display instead of the window

[crbender]

Summary

Selecting a specific app window in the source selector can still record the entire display on Windows.

Environment

• OS: Windows 10/11
• Build: packaged x64 app
• Capture mode: native Windows capture (WGC helper available)

Steps to Reproduce

1. Open the source selector.
2. Choose a single window:* source.
3. Start recording.
4. Review the output.

Actual Result

The recording captures the full monitor instead of the selected window.

Expected Result

When a window source is selected, recording should capture that specific window only.

Root Cause

The Windows native start path builds display-target config (displayId/bounds) and does not pass windowHandle to the WGC helper, even when the selected source is a window.

Proposed Fix

In Windows native recording setup:

1. Parse window:* source IDs into a window handle.
2. Set config.windowHandle when valid.
3. Only populate display targeting fields when no valid window handle exists.

Acceptance Criteria

1. Selecting window:* results in window-only capture on Windows native path.
2. Selecting screen:* continues to capture the display.
3. Regression coverage added for window-handle config selection logic.

[meiiie]

Closing as duplicate of #423 so the Windows selected-window capture bug is tracked in one canonical thread.

#422 is currently the stronger fix candidate because it also handles unresolved window:* IDs and the odd-size black-frame path. #424 remains the separate resize-during-recording follow-up.