Secure v2 user responses and access control

[fan yang (fanyangCS)]

Summary

• Restrict v2 user list access to admins and enforce self-or-admin checks on per-user reads and the legacy per-user password update route.
• Add centralized user response sanitization for v2 user responses, removing password data and confidential extension fields such as raw bounded-cluster tokens and SSH private keys while preserving safe metadata.
• Add focused regression coverage for access control and response redaction behavior.
• Keep the job-list user filter usable for non-admin portal sessions when the all-user API is unavailable.

Validation

• node -c src/rest-server/src/utils/userResponse.js
• node -c src/rest-server/src/controllers/v2/user.js
• node -c src/rest-server/src/routes/v2/user.js
• node -c src/rest-server/test/userResponseSecurity.js

Focused mocha/lint commands were attempted but local dependencies are not installed in this worktree:

• npm run mocha -- --grep "user response security" -> sh: 1: mocha: not found
• npm run lint -> sh: 1: eslint: not found

Notes

• Existing /api/v2/user and /api/v2/users aliases are preserved.
• Sanitization is applied at response construction; stored user extension data is not modified.