fix: add progress logging during silent render pipeline stages (#1220)

* fix: add progress logging during silent render pipeline stages

The render pipeline only updates progress at stage boundaries (5%, 10%,
25%), leaving multi-minute gaps with zero log output on low-memory
hardware. This adds log.info calls at key sub-steps within the three
silent stages:

- Probe stage (5%): browser launch, session initialization, duration
  discovery, media asset discovery, audio volume automation, video
  visibility window detection
- Video extraction (10%): per-video extraction progress
- Calibration (25%): browser launch, session initialization,
  per-frame calibration progress, final cost estimate

Also adds 30-second heartbeat timers for the two initializeSession
calls (probe and calibration) that can individually take minutes on
constrained hardware.

Closes #1218

* fix: resolve CI failures in typecheck, runtime seek test, and timeline test

- Make handleGsapMaterializeKeyframes optional in DomEditSessionSlice
  and use optional chaining at the call site (not yet wired)
- Update GSAP adapter seek test to expect nudge+seek pattern
  (totalTime with suppressEvents:true followed by actual seek)
- Fix Timeline canvas height test to use TRACK_H constant (48)
  instead of stale hardcoded value (72)

* refactor: extract helpers to meet 600-line file size limit

- App.tsx (603→594): extract StudioToast component
- useDomEditSession.ts (688→600): extract useGsapSelectionHandlers hook
- Timeline.tsx (614→557): extract useTimelineAssetDrop hook
- PropertyPanel.tsx (647→584): extract TimingSection to propertyPanelTimingSection

* style: fix formatting in TimelineToolbar

packages/studio/src/components/StudioToast.tsx

@@ -0,0 +1,18 @@
+interface StudioToastProps {
+  message: string;
+  tone?: "error" | "info";
+}
+
+export function StudioToast({ message, tone }: StudioToastProps) {
+  return (
+    <div
+      className={`absolute bottom-6 left-1/2 -translate-x-1/2 z-[91] px-4 py-2 rounded-lg border text-sm shadow-lg animate-in fade-in slide-in-from-bottom-2 ${
+        tone === "error"
+          ? "bg-red-900/90 border-red-700/50 text-red-200"
+          : "bg-neutral-900/95 border-neutral-700/60 text-neutral-100"
+      }`}
+    >
+      {message}
+    </div>
+  );
+}