fix(core,engine,producer): handle id-less media in sub-composition renders (#96)

## What

Move the id-less media fix into the shared timing compiler so producer can resolve durations for sub-composition videos before inlining, then carry the merged result through engine parsing, regression coverage, and the regression Docker image used in CI.

This PR now does five concrete things:

- assigns stable ids to id-less media in core `compileTimingAttrs()` so unresolved duration injection can target them
- keeps the engine-side `parseVideoElements()` support for `video[src]` plus the newer `data-duration` / natural-duration fallback from `main`
- makes producer prefer sub-composition media metadata over the later inlined-document parse when the same media id appears in both places
- makes `sub-composition-video` a runnable regression test by fixing its metadata and checking in the missing `output/compiled.html` snapshot
- removes the stale `pnpm-workspace.yaml` copy step from `Dockerfile.test`, so regression CI builds the Bun-based test image from the current workspace layout

## Why

- media without an explicit `id` could not participate in unresolved-duration resolution early enough
- producer could lose the resolved sub-composition timing by overwriting it with the later inlined parse
- the regression fixture intended to cover this case was not actually running in CI because its `meta.json` was incomplete and the required compiled snapshot was missing
- the regression image definition still expected a deleted `pnpm-workspace.yaml`, so GitHub Actions failed before the test shard could start

Putting the id-generation step in core makes the behavior reusable instead of relying on producer-only HTML patching.

## How

### Shared compiler

- core `compileTimingAttrs()` now auto-assigns stable ids to id-less `video` / `audio` tags
- those generated ids are returned in `unresolved`, so `injectDurations()` can add `data-duration` and `data-end` to the same media element later in the pipeline
- added core tests that cover auto-id assignment and duration injection for generated ids

### Producer

- when producer combines `subVideos` / `subAudios` with the media re-parsed from the final inlined HTML, it now lets the sub-composition metadata win
- this preserves the resolved/clamped timing already computed for nested media instead of overwriting it with the later parse
- `sub-composition-video` now has valid regression metadata and a checked-in `output/compiled.html` snapshot so CI actually executes it

### Engine

- resolved the merge conflict in `videoFrameExtractor` by keeping the broader `video[src]` parsing from this branch and the `data-duration` / natural-duration fallback that landed on `main`
- added a focused engine unit test for videos without ids

### CI image

- `Dockerfile.test` now copies only `package.json` and `bun.lock` at the workspace root before `bun install --frozen-lockfile`
- this matches the current monorepo layout and removes the obsolete pnpm-era dependency on `pnpm-workspace.yaml`

## Test plan

- [x] `bun run --filter @hyperframes/core test`
- [x] `bun run --filter @hyperframes/engine test`
- [x] `bun run --filter @hyperframes/producer test --update --sequential sub-composition-video`
- [x] `bun run --filter @hyperframes/producer test --sequential sub-composition-video`
- [x] Browser check with `agent-browser` against the compiled fixture page (`http://127.0.0.1:8123/compiled.html`)
- [x] Clean tracked-only Docker build of `Dockerfile.test` with the PR version of the file applied

## Notes

- Latest regression workflow is green on `main`, but before this PR the `sub-composition-video` fixture was being skipped by the harness rather than exercised end to end.
- The CI Docker fix was validated from a tracked-only export to avoid local untracked worktree artifacts affecting the result.

packages/producer/tests/sub-composition-video/meta.json

@@ -4,6 +4,8 @@
   "tags": ["video", "sub-composition", "regression"],
   "minPsnr": 25,
   "maxFrameFailures": 5,
+  "minAudioCorrelation": 0.0,
+  "maxAudioLagWindows": 120,
   "renderConfig": {
     "fps": 30
   }

packages/producer/tests/sub-composition-video/output/output.mp4

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:c08dcb89ed447e5bbff18214576ea7fff9ed6b5129cf12795e97199dff3d8e21
-size 3830455
+oid sha256:4a1ac6cb0517b8224364833754981228f1138848e4f70715065f64f939ab4253
+size 7277596