Redesign the Scenes tab around the screen and a search-first picker

[jdvmi00]

The Scenes tab read as a settings form: a long flat app list with a repeated trait on every row, three sections describing the selected zone, and a header that announced "No scene". This makes the screen the primary surface and the rail a picker.

• Header: "Workspace N · layout · local windows in every zone" until a scene is applied, then the scene name with "k of n placed" and, when needed, how many zones need attention. "Save as scene…" is the single action without a scene.
• Saved scenes are cards like the LAYOUTS list: a thumbnail with the apps drawn in their zones, the name, and "applied · apps · layout". Clicking applies; the delete shows on hover and keeps the inline confirm.
• One ZONES list (badge, icon, content, position such as "Top left", state) replaces CONTENT, ZONE and CHANGE TO. Positions come from which edges a zone touches; collisions fall back to the zone name.
• The picker under the selected zone auto-focuses a search. Enter assigns the top match, ↑ ↓ move it, Esc clears then closes, digits 1–9 select zones, and typing while the key handler has focus forwards into the search. Local windows and Empty are chips; groups are OPEN HERE with window titles, REMOTE DESKTOPS with the suffix stripped, and APPS. Hovering a row previews it in the selected card.
• Zone cards in Scenes mode show icon, name and state in the centre, "Local windows · fill order" when unassigned, Change… and Clear on the selected or hovered card, and an urgent outline plus Retry when something needs attention.
• Backend: the catalog carries each app's icon name and each saved scene's sources, and skips placeholder window classes such as Chromium's @@startup_wm_class. Icons resolve through Quickshell's icon provider, with a desktop-entry lookup for window classes. The pane keeps its app, scene and open-window lists by value so the two-second catalog poll no longer rebuilds rows.

Overlay IPC gains search, pick, hover and focusSearch; state reports query and matches. docs/SCENES.md and the changelog describe the new tab.

Validation: all local Lua, Python, and JavaScript CI suites passed, including new tests for the header, progress, picker helpers, position labels, and the placeholder filter; git diff --check and the manifest check passed. ShellCheck is unavailable locally; GitHub CI supplies it and the required native Windows display-policy check. Verified live on the shell: search plus Enter, digit selection in both focus states, the hover preview, position labels, an Empty assignment, an app assignment ending in needs-attention, save, delete, restore, and Esc handling.