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/blink_state.rs

@@ -0,0 +1,34 @@
+//! Shared blink state — a standalone Entity that ProjectBoxes read.
+//!
+//! By keeping blink state as a separate Entity (not a child of ProjectBox),
+//! cx.notify() on this entity only dirties views that .read(cx) it.
+//! Workspace and ProjectGrid do NOT read it → they stay cached.
+
+use gpui::*;
+use std::time::Duration;
+
+pub struct BlinkState {
+    pub visible: bool,
+    epoch: usize,
+}
+
+impl BlinkState {
+    pub fn new() -> Self {
+        Self { visible: true, epoch: 0 }
+    }
+
+    pub fn start(entity: &Entity<Self>, cx: &mut App) {
+        let weak = entity.downgrade();
+        cx.spawn(async move |cx: &mut AsyncApp| {
+            loop {
+                cx.background_executor().timer(Duration::from_millis(500)).await;
+                let ok = weak.update(cx, |state, cx| {
+                    state.visible = !state.visible;
+                    state.epoch += 1;
+                    cx.notify();
+                });
+                if ok.is_err() { break; }
+            }
+        }).detach();
+    }
+}