🔐 Add secure project link credentials

[Robdel12]

Summary

This PR layers the secure cloud auth flow on top of the CLI context work from #269.

• Separates user login from project upload credentials
• Adds vizzly project link <org>/<project> for minting project-scoped upload credentials
• Stores linked project tokens in macOS Keychain when available, with config-file fallback
• Uses linked project tokens for cloud uploads while keeping user JWTs for review actions
• Prevents failed project-token requests from consuming user refresh tokens
• Updates review commands so approval/comment actions require user auth instead of project tokens
• Adds credential-store coverage for Keychain/file fallback behavior

Testing

• node --test tests/commands/project.test.js tests/utils/config-loader.test.js tests/project/core.test.js tests/project/operations.test.js tests/commands/login.test.js tests/commands/review.test.js tests/api/client.test.js
• node --test tests/utils/project-link-store.test.js tests/commands/project.test.js tests/utils/config-loader.test.js tests/api/client.test.js tests/commands/review.test.js
• npm run lint
• npm run build
• git diff --check