test(prerender): add e2e coverage for notFoundBoundary on prerender routes - #438

… HITs (#669)

A bake-lane loader's nested promise that settled inside the capture window
was recorded as its RAW value; the HIT overlay handed that plain value to
consumers whose code is an unconditional use(data.x) - React #438, root
error boundary, whole page down (found live on a storefront PDP whose 165ms
price fetch won the quiet window because a concurrent loader kept the
Flight stream byte-active past it).

- loader-snapshot.ts: settled nested promises now record behind a
  $rangoLoaderSettled marker; overlayLoaderContainer rehydrates them as
  Promise.resolve(pinned). A capture-computed holes bit on the marker picks
  the rehydration path (fully-pinned resolves immediately; deep holes chain
  on the fresh promise) so HITs never rescan the pinned subtree. The root
  container still unwraps (elideNested owns nested marking - no root flag).
- Red->green: 7 unit regressions + /shell-cache/settled + /ppr-shell/settled
  e2e twins (dev + production, both apps).
- guardHydrationErrors hoisted to @shared/e2e with one canonical string
  list (unminified #438 text + [RootErrorBoundary]); the two suite-local
  copies had already drifted, which is how the regression e2e passed
  against broken code. waitForHydration keeps the error window in scope.
- parallel() DSL: dropped the inference-only TSlots generic in both type
  files - bare arrow slot handlers get a typed ctx (descriptor arrows still
  need an annotation; StaticHandlerDefinition.handler pollutes the union).
- skills/ppr + parallel, loader-container-bake design doc updated.