[codex] Add sticky note artifacts

[artpi]

Summary

• Add macOS sticky notes backed by private wp_guideline artifact posts tagged artifact, note, and sticky.
• Add Stickies menu controls, always-visible floating NSPanel notes, autosave, artifact opening, and first-line title editing.
• Reuse the WordPress.com guideline artifact flow for term resolution, list/create/update, plus quick overlay and drag-text shortcuts.

Validation

• git diff --check
• make CODESIGN_IDENTITY=- WPCOM_OAUTH_CLIENT_SECRET_FILE=.wpcom-oauth-client-secret
• Relaunched WP Workspace Dev.app