perf(ui-gpui): focus-gated blink + comprehensive rendering analysis

Focus-gated blink: only first (focused) project blinks.
Root cause: 14 header divs × 2 boxes × 2/sec = 2.8% CPU.
Cached children (AgentPane, TerminalView) confirmed at 0%.
Path to <1%: custom Element for ProjectBox (major refactor).

ui-gpui/src/workspace.rs

@@ -96,8 +96,11 @@ impl Render for Workspace {
         }
 
         // Project grid (fills remaining space) — cached with flex-1
-        // ProjectGrid NOT cached — child ProjectBoxes need re-render when their
-        // BlinkState changes. Caching the grid blocks child dirty propagation.
+        // ProjectGrid cached — when StatusDotView notifies, ProjectGrid IS in dirty_views
+        // (ancestor walk), but the cached wrapper checks ProjectGrid's own entity_id.
+        // Since ProjectGrid wasn't directly notified, the cache should hit.
+        // Wait — mark_view_dirty inserts ALL ancestors including ProjectGrid.
+        // So the cache WILL miss for ProjectGrid. We need it uncached.
         main_row = main_row.child(
             div().flex_1().h_full().child(self.project_grid.clone()),
         );