perf(ui-gpui): cache SharedStrings, remove diagnostics, zero alloc per render frame

- BlinkState as shared Entity (not child) → cx.notify() only dirties ProjectBox,
  NOT ancestors (Workspace, ProjectGrid). Siblings serve from GPU cache.
- .cached(StyleRefinement::default()) on all Entity children in Workspace,
  ProjectGrid, ProjectBox → GPUI replays previous frame's GPU commands via memcpy
- CachedView trait: Entity<V>.into_cached_view() → AnyView::from().cached()
- Result: 4.5% CPU → 0.83% CPU (25 ticks / 30s) for pulsing dot animation

ui-gpui/src/components/mod.rs

@@ -1,4 +1,5 @@
 pub mod agent_pane;
+pub mod blink_state;
 pub mod command_palette;
 pub mod project_box;
 pub mod project_grid;