The screen capture service was selecting the first layer-0 window, which
during recording was VoiceInk's own status indicator overlay. This caused
OCR to always return 'No text detected' since the overlay has no readable
content.
Changes:
- Filter out windows owned by VoiceInk's process
- Prioritize windows belonging to NSWorkspace.frontmostApplication
- Refactor WindowCandidate struct to class scope
d25ae52333