refactor: move config, CA install, and Google IP logic into ViewModel…

[KianMahmoudi]

What this PR does

Migrates HomeScreen business logic from Composables to a proper
MVVM architecture.

Changes:

• Created ConfigRepository and ConfigRepositoryImpl
• Created CaRepository and CaRepositoryImpl
• Added Hilt DI module binding both repositories
• Moved config save/load logic to HomeViewModel
• Moved Google IP auto-detect logic to HomeViewModel
• Moved CA certificate install logic to HomeViewModel
• HomeScreen now observes ViewModel state instead of doing
  direct ConfigStore calls

What stays in the UI layer (intentionally):

• attachBaseContext locale setup (too early for ViewModel)
• MhrvVpnService config reading (system component)
• Activity result launchers for VPN and CA install