demo-function: Playwright TS manifest discovery (sidecar + docgen annotations)

[cursor]

Summary

Follow-up to issue #47: support --manifest pointing at a Playwright .ts / .tsx spec without a separate YAML path argument.

Desired behavior

1. Sibling YAML auto-discovery: lesson.spec.ts → try lesson.spec.docgen.yaml and lesson.docgen.yaml.
2. Inline contract: Parse test.info().annotations.push({ type: "docgen", description: ... }) per test() block; support JSON.stringify({...}) (with trailing commas) and JSON string description.
3. Disambiguation: path.spec.ts::Test title or docgen demo-function --manifest path.spec.ts --grep "..." when multiple docgen annotations exist.
4. Merge rules: When YAML sidecar is used with kind: playwright, default demonstration.spec to the TS file and fill demonstration.grep from CLI/path::title when omitted.

Implementation

Tracked in branch cursor/ts-manifest-discovery-fcf7 (PR to follow).