fix(engine,producer,cli): close review gaps in sub-timeline fail-fast

Address PR #2045 review feedback:
- Share a SubTimelineWaitOutcome type (engine) end-to-end instead of
  widening to string across CapturePerfSummary / RenderPerfSummary /
  telemetry, so the three layers can't drift.
- Dedupe scriptLoadFailures on push — a 4xx response and its trailing
  requestfailed both recorded the same URL, doubling the failed-URL
  list in the fail-fast warning.
- Thread the sub-timeline-wait outcome into render_error (not just
  render_complete): a render that fail-fasts and then fails downstream
  (pollVideosReady, extract, encode) previously dropped this signal on
  the floor. dedupPerfs is now function-scoped so the catch path can
  read it, same treatment as the existing captureAttempts array.

packages/engine/src/index.ts

@@ -40,6 +40,7 @@ export type {
   CaptureResult,
   CaptureBufferResult,
   CapturePerfSummary,
+  SubTimelineWaitOutcome,
 } from "./types.js";
 
 // ── Configuration ──────────────────────────────────────────────────────────────