fix(ui): fix drag-and-drop on Windows and catalog rail layout

[thcp]

Summary

• dragDropEnabled: false in tauri.conf.json — WebView2 was intercepting OS-level drag events before they reached the HTML page, silently swallowing all dragover/drop events. This is the documented requirement for HTML5 DnD on Windows in Tauri v2.
• Catalog rail background fills full height — the rail column was auto-placing catalog-main into an implicit grid row in the collapsed state, stealing height from the 1fr row and leaving the rail background short. Fixed by pinning both children to explicit grid-column/grid-row and adding grid-template-rows: 1fr to the catalog grid.
• dropOnFolder / getDraggedTrackId hardening — accepts an explicit trackId argument and a text/plain fallback for WebView2's cross-origin dataTransfer restrictions.
• Restore from trash — dragging a track from the trash view onto the Library rail button now restores it to the first non-trash folder and switches back to library view.

Test plan

• Drag a song card from Unsorted to a user folder — moves cleanly
• Drag a song card to the Trash rail button — moves to trash
• Switch to Trash view, drag a track back onto the Library rail button — restores to Unsorted, view switches to Library
• Collapse the library panel — rail background fills full height with no lighter strip below About
• Expand the library panel — layout correct, no regression