Recordings window: thumbnail grid, search and sort

[nftechie]

Context

The Recordings window (⌘L) is a plain list with small 128×80 thumbnails, no search, and newest-first order only. Once you have dozens of recordings, finding one is slow. There are also two small issues worth fixing along the way:

• The window reloads on NSWindow.didBecomeKeyNotification from any window, re-reading every project.json each time an editor or Settings window gets focus.
• The empty state always says "Recordings are saved to ~/Movies/Recordings", even when a custom folder is set in Settings.

Where to look

• Sources/Snapcap/Views/LibraryView.swift: LibraryView, LibraryRow, loadThumbnail(for:) (which uses AVAssetImageGenerator at min(1, duration / 2)), the context menu and the trash confirmation.
• Sources/SnapcapCore/Model/RecordingLibrary.swift: entries() (sorted newest first), Entry.exportURL and rootURL.
• Sources/Snapcap/Views/EditorView.swift: EditorModel.rename(to:), if you want to offer Rename from the grid too.
• Sources/Snapcap/App/AppDelegate.swift: showLibrary() creates the window (760×560, minimum 520×360).
• Sources/Snapcap/Views/Components.swift: formatDuration and the Brand colors.

Proposal

• Show a grid of cards in a LazyVGrid with adaptive columns of about 220 pt. Each card has a 16:10 thumbnail, name, duration, date and export status. Keep a list mode behind a toggle stored in @AppStorage.
• Add .searchable filtering by name and source title, case- and diacritic-insensitive.
• Add a sort menu (newest, oldest, longest, name), and remember the choice.
• Cache thumbnails in an NSCache keyed by folder and lastExport.date, so scrolling and reloads don't regenerate them.
• Keep every existing context-menu action. Double-click and Return open a recording, and ⌘⌫ moves it to the Trash with the existing confirmation.
• Reload only when the Recordings window itself becomes key, or watch the folder with a DispatchSource.
• Put the filter and sort logic in a small pure function in SnapcapCore so it can be unit tested.

Acceptance criteria

• Grid and list modes, remembered across launches.
• Search filters as you type, with a "No matches" empty state. The no-recordings empty state shows the actual recordings folder.
• Sort options work and are remembered.
• Thumbnails load lazily and are cached, and scrolling through 100+ recordings stays smooth. To generate test data: for i in $(seq 1 120); do snapcap-cli fixture /tmp/snapcap-lib/Sessions/fixture-$i --seconds 2; done, then launch with SNAPCAP_LIBRARY=/tmp/snapcap-lib.
• Keyboard: arrow keys move the selection, Return opens, and ⌘⌫ moves to the Trash.
• Unit tests cover filtering and sorting.