- Add UserSudoController with GET and POST /users/sudo/verify routes
- Create verify.html.heex template for TOTP verification form
- Only accept TOTP codes (6 numeric digits), reject recovery codes
- Update grant_sudo_mode to set authenticated_at virtual field
- Exclude /users/sudo paths from return_to overwriting
- Add comprehensive controller tests (12 test cases)
- Verify redirect behavior, error handling, and session management
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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
The plug was incorrectly placed in the endpoint, causing it to run on
all requests including APIs. Moved to :browser pipeline where it belongs,
and removed redundant fetch_session call since the pipeline handles it.
