fix: user controller - add swagger annotation, exception handling controller->service

[ssoheeh]

Features

• user
  • user controller refactor (resolves: refactor: user & oauth #20)

Chore

• user controller swagger annotation 추가
• exception handling controller -> service layer 에서 처리

[codecov]

Codecov Report

Attention: Patch coverage is 6.25000% with 15 lines in your changes missing coverage. Please review.

Project coverage is 23.36%. Comparing base (b120ccd) to head (1c87cd1).
Report is 5 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...va/com/server/domain/user/service/UserService.java	8.33%	11 Missing ⚠️
.../server/domain/user/controller/UserController.java	0.00%	4 Missing ⚠️

@@             Coverage Diff              @@
##               main      #35      +/-   ##
============================================
- Coverage     24.86%   23.36%   -1.50%     
+ Complexity       40       38       -2     
============================================
  Files            39       39              
  Lines           366      368       +2     
  Branches         17       17              
============================================
- Hits             91       86       -5     
- Misses          275      282       +7     

Components	Coverage Δ
user	∅ <ø> (∅)

Files with missing lines	Coverage Δ	Complexity Δ
.../server/domain/user/controller/UserController.java	9.09% <0.00%> (+4.09%)	1.00 <0.00> (ø)
...va/com/server/domain/user/service/UserService.java	58.82% <8.33%> (-41.18%)	9.00 <1.00> (-1.00)

... and 1 file with indirect coverage changes

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