fix: stabilize studio preview and runtime sync (#389)

## Summary
Stabilize the Studio preview/runtime path so timeline data, preview rendering, and thumbnails stay in sync.

This PR includes:
- preview hot-refresh without remounting the iframe
- runtime duration/timeline fixes so Studio stops drifting from playback state
- thumbnail and selector-based preview fixes
- local Studio runtime serving and player-resolution fixes so dev/CI do not depend on prebuilt player artifacts
- tests around preview identity and thumbnail/runtime behavior

## Why This PR Exists
This is the foundation layer for timeline editing. Without it, the editor was prone to:
- iframe remount flashes after saves
- duration mismatches between preview and timeline
- stale or incorrect thumbnails
- CI/test failures when `@hyperframes/player` artifacts were not prebuilt

## Verification
- `bun run --filter @hyperframes/studio test`
- `bun run --filter @hyperframes/studio typecheck`
- `bun run --filter @hyperframes/core typecheck`
- `bunx oxlint packages/cli/src/server/studioServer.ts packages/core/src/runtime/timeline.ts packages/core/src/runtime/timeline.test.ts packages/core/src/studio-api/routes/thumbnail.ts packages/core/src/studio-api/routes/thumbnail.test.ts packages/core/src/studio-api/types.ts packages/studio/src/components/nle/NLELayout.tsx packages/studio/src/components/nle/NLEPreview.tsx packages/studio/src/components/nle/NLEPreview.test.ts packages/studio/src/player/components/CompositionThumbnail.tsx packages/studio/src/player/components/Player.tsx packages/studio/src/player/hooks/useTimelinePlayer.ts packages/studio/src/player/store/playerStore.ts packages/studio/vite.config.ts`
- `bunx oxfmt --check packages/cli/src/server/studioServer.ts packages/core/src/runtime/timeline.ts packages/core/src/runtime/timeline.test.ts packages/core/src/studio-api/routes/thumbnail.ts packages/core/src/studio-api/routes/thumbnail.test.ts packages/core/src/studio-api/types.ts packages/studio/src/components/nle/NLELayout.tsx packages/studio/src/components/nle/NLEPreview.tsx packages/studio/src/components/nle/NLEPreview.test.ts packages/studio/src/player/components/CompositionThumbnail.tsx packages/studio/src/player/components/Player.tsx packages/studio/src/player/hooks/useTimelinePlayer.ts packages/studio/src/player/store/playerStore.ts packages/studio/vite.config.ts`

## Stack
- base of stack
- followed by `feat: add studio timeline editing`
- followed by `fix: smooth scrubber end seeking`

packages/cli/src/server/runtimeSource.ts

@@ -0,0 +1,11 @@
+export async function loadRuntimeSourceFallback(): Promise<string | null> {
+  try {
+    const mod = await import("@hyperframes/core");
+    if (typeof mod.loadHyperframeRuntimeSource === "function") {
+      return mod.loadHyperframeRuntimeSource();
+    }
+  } catch (err) {
+    console.warn("[studio] Failed to load runtime source fallback:", err);
+  }
+  return null;
+}