fix(studio): polish media panel UX and preserve selection on undo

- Move Timing + Media sections above Layout in the Design panel
- Remove LayerTree from Design panel (redundant with Layers tab)
- Replace Rate and Media Start with sliders matching Volume's UX
- Replace Position DetailField with SelectField to match Fit height
- Remove Poster field (not useful for HyperFrames compositions)
- Show absolute filesystem path for Source (resolves symlinks)
- Add Copy button for source path with checkmark feedback
- Preserve element selection on undo/redo instead of clearing it

packages/studio/src/hooks/useAppHotkeys.ts

@@ -57,7 +57,6 @@ export function useAppHotkeys({
   handleTimelineElementDelete,
   handleDomEditElementDelete,
   domEditSelectionRef,
-  clearDomSelectionRef,
   editHistory,
   readOptionalProjectFile,
   readProjectFile,
@@ -116,12 +115,10 @@ export function useAppHotkeys({
       return;
     }
     if (result.ok && result.label) {
-      clearDomSelectionRef.current();
       await syncHistoryPreviewAfterApply(result.paths);
       showToast(`Undid ${result.label}`, "info");
     }
   }, [
-    clearDomSelectionRef,
     editHistory,
     readHistoryProjectFile,
     showToast,
@@ -141,12 +138,10 @@ export function useAppHotkeys({
       return;
     }
     if (result.ok && result.label) {
-      clearDomSelectionRef.current();
       await syncHistoryPreviewAfterApply(result.paths);
       showToast(`Redid ${result.label}`, "info");
     }
   }, [
-    clearDomSelectionRef,
     editHistory,
     readHistoryProjectFile,
     showToast,