fix: capture-mode polish for studio & presets + pausable render loop (#469)

* fix(editor): keep snapshot pitch out of preset thumbnail capture

The capture overlay's snapshot hint and 'Take snapshot' shutter label
rendered in every capture variant, clashing with the save-as-preset
flow's own 'Frame your item — click Capture' banner. Gate them on the
existing isPreset discriminator and label the shutter 'Capture' there.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* feat(viewer): renderPaused flag suspends the frame loop

Hosts that fully cover the canvas (e.g. the studio gallery overlay) can
set renderPaused to stop FrameLimiter's RAF loop — a heavy animated
scene otherwise keeps starving the GPU behind the overlay and makes it
stutter.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(editor): drop the crop/format HUD in preset capture

The pills crowded the save-as-preset banner and repeat what the fixed
square frame already shows.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(editor): no contextual shortcut hints in the studio workspace

Holding Shift surfaced select-mode/snapping hints over the studio
compose panel and gallery, where there is no scene selection or tool to
act on.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/viewer/src/store/use-viewer.ts

@@ -49,6 +49,10 @@ type ViewerState = {
   isExporting: boolean
   setExporting: (value: boolean) => void
 
+  /** Suspend the render loop while the canvas is fully covered (e.g. studio gallery). */
+  renderPaused: boolean
+  setRenderPaused: (value: boolean) => void
+
   shading: RenderShading
   shadingByContext: Partial<Record<RenderContext, RenderShading>>
   setShading: (shading: RenderShading) => void
@@ -233,6 +237,9 @@ const useViewer = create<ViewerState>()(
       isExporting: false,
       setExporting: (value) => set({ isExporting: value }),
 
+      renderPaused: false,
+      setRenderPaused: (value) => set({ renderPaused: value }),
+
       shading: 'rendered',
       shadingByContext: {},
       setShading: (shading) =>