fix(studio): keep the preview alive when the window is tight (#3091)

Panel sizes are reconciled against the window on every resize, with the preview holding a 360x200 floor that panels yield to before it gives.

Measured preview pane: 760px window 192 -> 433, 560px window 2 -> 516. Windows at or above 1280px are unchanged.

- fitPanels owns the who-yields decision for both axes
- panel caps are window-relative, replacing a flat 600px inspector cap
- below 860 the sidebar rails, below 700 the inspector collapses too
- auto-collapse is derived render state and never writes leftCollapsed
  (localStorage) or rightCollapsed (synced into the shareable URL)
- the rail and header toggles act on the effective state, so neither is a
  dead click that silently persists a collapse the user never asked for

packages/studio/src/contexts/PanelLayoutContext.tsx

@@ -17,9 +17,10 @@ export function PanelLayoutProvider({
     rightWidth,
     adjustPanelWidth,
     leftCollapsed,
-    setLeftCollapsed,
     rightCollapsed,
     setRightCollapsed,
+    effectiveLeftCollapsed,
+    effectiveRightCollapsed,
     rightPanelTab,
     setRightPanelTab,
     rightInspectorPanes,
@@ -41,9 +42,10 @@ export function PanelLayoutProvider({
       rightWidth,
       adjustPanelWidth,
       leftCollapsed,
-      setLeftCollapsed,
       rightCollapsed,
       setRightCollapsed,
+      effectiveLeftCollapsed,
+      effectiveRightCollapsed,
       rightPanelTab,
       setRightPanelTab,
       rightInspectorPanes,
@@ -59,9 +61,10 @@ export function PanelLayoutProvider({
       rightWidth,
       adjustPanelWidth,
       leftCollapsed,
-      setLeftCollapsed,
       rightCollapsed,
       setRightCollapsed,
+      effectiveLeftCollapsed,
+      effectiveRightCollapsed,
       rightPanelTab,
       setRightPanelTab,
       rightInspectorPanes,