Add SSH keypair reset functionality in User Settings once backend API is available

## Objective

Add SSH keypair reset/revocation functionality in the WebUI User Settings page.

## Context

- Current SSH keypair UI allows registration and viewing but has no reset or revoke option
- This feature is **blocked by** BA-5398 (backend API for SSH keypair reset/revocation)
- Once the backend API is available, implement:
1. "Reset keypair" button that calls the new backend API
1. "Revoke keypair" option to remove the registered keypair
1. Confirmation dialogs to prevent accidental actions

## Dependency

- **Blocked by**: BA-5398 (backend API for SSH keypair reset)

## Related Files

- SSH keypair management components in User Settings
- `SSHKeypairManagementPanel` and related components

## Effort & Risk

- **Effort**: Low-Medium (straightforward UI addition once API is available)
- **Risk**: Low (additive feature)

## Status

**Pending** — waiting for backend API (BA-5398) to be implemented first.

JIRA Issue: FR-2374