feat(studio): per-composition render button in compositions tab (#874)

* feat(studio): add per-composition render button in compositions tab

Thread composition path through the full render pipeline so individual
compositions can be rendered independently from the studio UI.

- Add download icon button on each comp card (visible on hover)
- Accept `composition` field in POST /projects/:id/render
- Pass composition as `entryFile` to the producer's createRenderJob
- Make the Export button in the Renders panel composition-aware
  (renders the active composition instead of always index.html)

* fix(studio): make composition render buttons always visible

The hover-only opacity made them undiscoverable.

* fix(studio): address PR review — CLI adapter, path guard, a11y, tests, settings sync

- Wire `composition` → `entryFile` in CLI studio adapter (studioServer.ts)
  so `hyperframes preview` renders the correct composition, not always index.html
- Add path-traversal guard: reject composition paths that resolve outside projectDir
- Add `aria-label` to the icon-only render button for screen readers
- Add 4 tests: forwarding, empty/missing → undefined, path-traversal → 400
- Persist render settings (format/quality/fps) to localStorage so comp card
  buttons use the same settings as the Export panel

* refactor(studio): extract render settings persistence to own module

Move getPersistedRenderSettings/persistRenderSettings out of
RenderQueue.tsx into renderSettings.ts so code-splitting the
component doesn't drag along the helper.

packages/studio/src/components/StudioRightPanel.tsx

@@ -198,7 +198,17 @@ export function StudioRightPanel({
                   onClearCompleted={renderQueue.clearCompleted}
                   onStartRender={async (format, quality, resolution, fps) => {
                     await waitForPendingDomEditSaves();
-                    await renderQueue.startRender({ fps, quality, format, resolution });
+                    const composition =
+                      activeCompPath && activeCompPath !== "index.html"
+                        ? activeCompPath
+                        : undefined;
+                    await renderQueue.startRender({
+                      fps,
+                      quality,
+                      format,
+                      resolution,
+                      composition,
+                    });
                   }}
                   compositionDimensions={compositionDimensions}
                   isRendering={renderQueue.isRendering}