[UX Improvement]: Prompt user to restart connection when settings are modified during an active session

### Description
Currently, if a user modifies core configurations (such as Protocol, Scan Mode, Obfuscation, or Conduit) while the VPN is actively connected, the application does not notify them that a reconnection is required for the new settings to take effect.

This leads to user confusion, as they might assume the changes are applied immediately to the active tunnel, while in reality, they are operating on the old configuration until the next manual disconnect/reconnect cycle.

### Proposed Solution
Implement a visual notification (such as a Flutter `SnackBar` or a persistent UI Banner) that appears immediately after a setting is changed while the VPN state is `Connected`.

This prompt should:
1. Clearly state that a restart is required to apply the changes.
2. Include a convenient **[Restart Now]** / **[Reconnect]** action button right next to the message, allowing the user to seamlessly restart the tunnel with a single tap.

### Example UX Flow
1. User is actively connected.
2. User navigates to Settings and changes "Obfuscation" from *Off* to *Light*.
3. A Snackbar pops up at the bottom:
*(Icon) "Settings saved. Restart connection to apply changes."* -> **[RESTART]**
4. Tapping the `[RESTART]` button automatically stops the current service and initializes a new connection with the updated config.

### Why This Matters
It eliminates ambiguity, improves the overall user experience, and removes the extra friction of manually navigating back to the home screen to turn the VPN off and on again.

Start by locating the Flutter settings screens, the Connected VPN state, and the existing disconnect/reconnect entry point. Trace how setting changes are saved and how the tunnel is restarted. Done means changing Protocol, Scan Mode, Obfuscation, or Conduit while connected shows a clear restart prompt with a working action that applies the new configuration.

Written by the indexing model from the issue text.