Prevent assigning Super Administrator as the registration default role

[ruibaby]

What type of PR is this?

• Feature
• Bug fix
• Improvement
• Cleanup
• Documentation

What this PR does / why we need it:

The registration default-role selector currently allows selecting Super Administrator, which can give newly created users unrestricted permissions.

Add an optional excludedNames list to roleSelect and exclude super-role from the registration default-role options. Reject this role before user creation through password registration, OAuth2 registration, and the Console user creation endpoint, including when it is already present in persisted settings.

Reproduction covered by regression tests: configure user.defaultRole as super-role and invoke these creation paths. Before the fix, they accept the role; after the fix, they return the existing default-role configuration error before creating a user.

Which issue(s) this PR fixes:

None.

Special notes for your reviewer:

Developed with Codex assistance.

Validation passed:

• 113 focused backend tests covering UserServiceImpl, OAuth2RegistrationService, and UserEndpoint.
• 5 roleSelect tests covering omitted, empty, single-role, and multiple-role exclusions.
• Frontend application type checking and targeted ESLint.
• Java Spotless and frontend formatting checks.
• git diff --check.

Browser validation and the full test suite were not run.

Does this PR introduce a user-facing change?

action required: 注册默认角色不再支持选择超级管理员。若此前已将默认角色设为超级管理员，请改选其他角色，否则注册和使用默认角色创建用户将被阻止。

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.30%. Comparing base (42c374d) to head (a6c9777).
⚠️ Report is 812 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #10357      +/-   ##
============================================
+ Coverage     59.55%   67.30%   +7.74%     
- Complexity     3812     5437    +1625     
============================================
  Files           677      769      +92     
  Lines         23248    27336    +4088     
  Branches       1500     1918     +418     
============================================
+ Hits          13846    18399    +4553     
+ Misses         8764     8021     -743     
- Partials        638      916     +278     

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