feat: Implement setup screen and login logic

- Add SetupScreen with UI for server URL, username, and password input.
- Make SetupScreen the initial screen in the navigation graph.
- Implement secure credential storage using EncryptedSharedPreferences.
- Create CredentialsRepository and AuthRepository to manage credentials and auth tokens.
- Add LoginUseCase to handle the business logic for logging in.
- Implement a temporary Retrofit client in ItemRepository to handle login against a user-provided URL.
- Integrate login logic into SetupViewModel.
- Update all relevant project documentation and DI modules.

tech_spec/tech_spec.txt

@@ -117,6 +117,7 @@
         <USE_CASE id="uc_delete_item" file_ref="domain/src/main/java/com/homebox/lens/domain/usecase/DeleteItemUseCase.kt" />
         <USE_CASE id="uc_get_all_labels" file_ref="domain/src/main/java/com/homebox/lens/domain/usecase/GetAllLabelsUseCase.kt" />
         <USE_CASE id="uc_get_all_locations" file_ref="domain/src/main/java/com/homebox/lens/domain/usecase/GetAllLocationsUseCase.kt" />
+        <USE_CASE id="uc_login" file_ref="domain/src/main/java/com/homebox/lens/domain/usecase/LoginUseCase.kt" />
 
         <!-- UI Screens -->
         <UI_SCREEN id="screen_dashboard" file_ref="app/src/main/java/com/homebox/lens/ui/screen/dashboard/DashboardScreen.kt" />
@@ -126,5 +127,6 @@
         <UI_SCREEN id="screen_labels_list" file_ref="app/src/main/java/com/homebox/lens/ui/screen/labelslist/LabelsListScreen.kt" />
         <UI_SCREEN id="screen_locations_list" file_ref="app/src/main/java/com/homebox/lens/ui/screen/locationslist/LocationsListScreen.kt" />
         <UI_SCREEN id="screen_search" file_ref="app/src/main/java/com/homebox/lens/ui/screen/search/SearchScreen.kt" />
+        <UI_SCREEN id="screen_setup" file_ref="app/src/main/java/com/homebox/lens/ui/screen/setup/SetupScreen.kt" />
     </IMPLEMENTATION_MAP>
 </PROJECT_SPECIFICATION>