Add 'Export rules' and 'Import rules' feature

[yogesh-7]

📦 Import / Export Rules

Users who reinstall the app or switch devices currently lose all their per-app rules. Add the ability to export and import the rule set as a JSON file.

Requirements

Export

• Button in SettingsScreen.kt: Export rules
• Serialize all AppRule entries from Room into JSON
• Save via ACTION_CREATE_DOCUMENT system picker
• Format suggestion:

  {
    "version": 1,
    "exportedAt": "2026-04-15T10:00:00Z",
    "rules": [
      { "packageName": "com.example", "wifiAllowed": true, "mobileAllowed": false }
    ]
  }

Import

• Button: Import rules
• Open file via ACTION_OPEN_DOCUMENT
• Validate JSON schema
• Confirm dialog: "This will overwrite your current rules. Continue?"
• Upsert rules into Room
• Trigger VPN tunnel rebuild

Edge Cases

• Invalid JSON → show error toast
• Missing packages (app uninstalled) → skip silently or log
• Schema version mismatch → show friendly error

Hints

• Use kotlinx.serialization (add as dependency)
• Access repository via SettingsViewModel
• File IO with ActivityResultContracts.CreateDocument / OpenDocument

Medium difficulty — great for someone wanting to touch persistence, UI, and Android file APIs!