Backend Users: Add rate limiting on write endpoints

[aji70]

Description (Backend)

Backend module Users (users-module). Add rate limiting on write endpoints.

Tasks

• Implement the change in the relevant code paths
• Wire or persist state where the feature touches runtime behavior
• Add tests (unit, integration, and/or contract/UI as appropriate)

Additional Requirements

• Handle stale, disconnected, or invalid states gracefully where applicable
• Follow existing patterns in this repository (linting, modules, security)

Acceptance Criteria

• Behavior is covered by tests and documented where APIs changed
• No regressions in closely related user or API flows

[brentthomas248]

I opened PR #1347 for this issue.

The patch adds ThrottlerGuard coverage to UsersController, limits create/update/delete user write endpoints to 5 requests per minute, documents 429 responses, and adds focused metadata coverage confirming write endpoints are throttled while read endpoints stay unthrottled.

Verified with:

• npm test --prefix backend -- users.throttle.spec.ts --runInBand
• npm test --prefix backend -- users.controller.spec.ts users.throttle.spec.ts --runInBand
• npm test --prefix backend -- users-module --runInBand
• changed-file ESLint and git diff --check

A full tsc probe is still blocked by the existing unrelated syntax error in src/social-link/social-links.controller.spec.ts:293.