feat: add source-led Copywriter plugin

[letsrokk]

Summary

Add Copywriter 0.1.0 to the Codex and Claude catalogs with one shared skill tree. The router and five writing skills transform repository evidence or substantive author material into taglines, READMEs, landing pages, pitch decks, and articles. Topic-only article requests require source notes; claims, transformations, and asset provenance remain traceable.

Includes a static HTML generator, bundled editable PptxGenJS renderer with notes and real chart data, and separate portable/Codex/Claude package assembly. Runtime dependencies are bundled; CI installs contributor dependencies for validation. Generated output and private review records stay outside release packages.

Verification

• Fresh npm test: 36 tests pass; npm run validate passes.
• Fresh Copywriter test and validation entrypoints: 4 tests pass; pinned schema, skill references, syntax, and reproducible bundle checks pass.
• All six skills pass the local skill validator. Codex scaffold validation passes; Claude Code 2.1.268 validates the native package with an optional-author warning.
• Local demonstrations produced an editable eight-slide PPTX, PDF and slide previews, HTML page, and illustrated article. Impress opened editable text; all PDF slides were inspected. Safari desktop and 390-pixel hero previews were inspected.

Remaining release checks

This is a draft because installed Codex/Claude skill invocation, full narrow-page and keyboard review, application accessibility checks, and independent human editorial evaluation remain unverified. The recorded agent evaluations are not evidence of marketing effectiveness.

See plugins/copywriter/tests/evaluation.md and plugins/copywriter/packaging/compatibility.md for scope and limits. Generated demonstrations are local review artifacts and are not included in this PR.