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.

app/build.gradle.kts

@@ -82,6 +82,9 @@ dependencies {
     // [DEPENDENCY] Logging
     implementation(Libs.timber)
 
+    // [DEPENDENCY] Security
+    implementation(Libs.securityCrypto)
+
     // [DEPENDENCY] Testing
     testImplementation(Libs.junit)
     androidTestImplementation(Libs.extJunit)