Add: add Storage Model

[happycastle114]

FlutterSecureStorage에 토큰 저장 후 매번 불러오기 추가

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 31 lines in your changes missing coverage. Please review.

Project coverage is 38.75%. Comparing base (5896c05) to head (e8f00c9).

Files with missing lines	Patch %	Lines
lib/providers/auth_model.dart	0.00%	16 Missing ⚠️
lib/extensions/storage_model.dart	0.00%	12 Missing ⚠️
lib/pages/login_page.dart	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #208      +/-   ##
==========================================
- Coverage   39.00%   38.75%   -0.25%     
==========================================
  Files          80       81       +1     
  Lines        4879     4910      +31     
==========================================
  Hits         1903     1903              
- Misses       2976     3007      +31     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.