refactor: remove macOS vibrancy support and unify glass surfaces

Drops the macOS vibrancy toggle, IPC, and related settings copy
Updates dialogs, popovers, tooltips, and dropdowns to use shared glass styles
Adds sticky header fade behavior to model picker and sidebar lists

packages/ui/src/components/chat/work-status/DOCUMENTATION.md

@@ -25,6 +25,8 @@ It is **not** a context-panel surface. It is not registered in
 `lib/surfaces/registry.ts`, has no rail icon, no tab, no persisted width and no
 resizer. It is a card floating inside the chat column — rounded border, faint
 fill, its own margin — rather than a docked pane flush against the window edge.
+When it overlays the transcript, it uses the shared `oc-glass-panel` surface;
+the inline card keeps its lighter, non-blurred fill instead.
 
 ## Placement