Add Vercel project import skill

[wentsul]

Summary

• add an approval-gated vercel-project-import skill
• document discovery via vercel projects import-candidates
• cover project creation, root settings, Git connection, optional secret-safe environment setup, optional attachment of existing connectors, and Git-native production deployment
• each stage can be applied, skipped, or deferred

Testing

• bun run build:manifest
• bun run scripts/generate-catalog.ts
• bun run build:manifest:check
• bun run validate

bun run validate passes with the existing offline llms.txt coverage warning.