Add in-game preview capture workflow

[NooriSeiros]

Summary

• Adds a Capture from Game action to the existing preview image workflow.
• Places a transparent selection overlay over the game window; drag selects the preview area, right mouse temporarily passes control back to the game camera, and Esc cancels safely.
• Shows the captured crop for confirmation with Recapture and Use This Preview actions.
• Validates temporary capture paths, limits oversized images, removes stale crop metadata, and backs up the previous preview before replacement.
• Returns a clear unsupported-platform error outside Windows.

Validation

• npm run build
• cargo check
• cargo test preview_capture --lib (2 passed)
• Targeted ESLint check (no new errors; one existing warning remains in ModPreview.tsx)