[ctawiah]

Context

All callers now use descriptor-backed repository sources. The Phase 1 whole-file reference bridge is unused.

What changes

• Remove the old plain Markdown adapter bridge.
• Remove front-matter reference fields and rendering.
• Remove old manifest reference metadata.
• Remove old linked-file publication and watch paths.
• Keep only descriptor-backed source APIs.
• Update tests for the final API.

Phase 1 front matter ref -> removed
.ref.yaml descriptor -> retained

Design notes

• This cleanup lands last because it removes pre-existing APIs.
• It adds no replacement bridge or temporary compatibility code.
• The 15-file cutover is one compile dependency cluster.

Review focus

• Does any caller still use the old API?
• Is the final tree identical to the completed adapter implementation?

Verification

• make build
• go test ./...
• Repository lint
• Relevant race tests
• Final tree comparison against the saved implementation

Related changes

1. ctawiah/sync-projection-core-3bbf: projection and problem core
2. ctawiah/sync-reference-core-3bbf: reference registry and Markdown
3. ctawiah/sync-structured-adapters-3bbf: structured adapters
4. ctawiah/sync-provider-profiles-3bbf: provider profiles
5. ctawiah/sync-python-adapter-3bbf: Python adapter
6. ctawiah/sync-typescript-adapters-3bbf: TypeScript and JavaScript adapters
7. ctawiah/sync-descriptor-storage-3bbf: descriptor storage
8. ctawiah/sync-source-publication-3bbf: source compilation and publication
9. ctawiah/sync-source-planner-3bbf: planner integration
10. ctawiah/sync-descriptor-detach-3bbf: descriptor detach
11. ctawiah/sync-link-preparation-3bbf: link preparation
12. ctawiah/sync-link-command-3bbf: link commands
13. This PR: Phase 1 cleanup