Support Vercel deployments and local secret files

[unix2dos]

Existing Vercel Hobby applications can now deploy through Ship while retaining their production Secrets. The CLI and local webpage share ownership and plan checks, deployment markers, status checks, and recovery of the original deployment after an uncertain response.

Application secrets that users choose to save live in owner-only plaintext files under ~/.ship, separate from ordinary project records. The tool preserves older local state and reports unreadable database targets as unverified. Vercel Secret updates omit the immutable key field; definite validation rejection and unknown outcomes are handled separately.

Validation:

• Local Go race tests, go vet, JavaScript syntax, fresh-install smoke checks, and state migration passed.
• Two real Go container deployments through Ship passed HTTP/PostgreSQL checks and retained existing data after the source update. Runtime logs were checked for known credentials. Business Secret metadata did not change.
• Synthetic Secret create/update/delete checks reproduced the immutable-key error and verified the corrected request. See validation/results/ship-vercel-acceptance.json and validation/results/vercel-secret-update-diagnosis.json.
• Adds Linux/macOS CI and an independent-user trial checklist.

This alpha manages existing Vercel Hobby + Neon Free resources for personal noncommercial use. Windows, resource creation, and independent-user acceptance remain pending.