request ACCESS_LOCAL_NETWORK when enabling open proxy on all interfaces

[munzzyy]

Fixes #1743

The "Open Proxy on All Interfaces" setting makes Tor bind its SOCKS port to 0.0.0.0 (TorConfig.kt), which on Android 17 needs the ACCESS_LOCAL_NETWORK permission. Right now we only ever request that permission from the kindness mode UPnP dialog, so flipping this setting on an API 37 device just produces a proxy that nothing on the LAN can actually reach - no prompt, no error, it just doesn't work.

What this does:

• Moved needsAccessLocalNetworkPermission() out of UPnPDialogFragment and into NetworkUtils, so it's shared instead of duplicated. UPnPDialogFragment and SnowflakeProxyWrapper now call the shared version.
• SettingsPreferenceFragment now hooks the "Open Proxy on All Interfaces" checkbox: turning it on triggers a permission request first (same grant / deny / "permanently denied -> app settings" flow the kindness dialog already uses), and the checkbox only gets checked once the permission is actually granted.
• TorConfig.build() falls back to a localhost-only SOCKSPort if the preference is on but the permission isn't (e.g. revoked after the fact in system settings), so we never emit a 0.0.0.0 config nothing can reach.
• One new string for the permission rationale toast.

Verified by reading through the existing kindness-mode permission flow and mirroring it exactly, and by checking every call site of the old UPnPDialogFragment.needsAccessLocalNetworkPermission (there were two: the dialog itself and SnowflakeProxyWrapper) to make sure both got updated. I don't have a Java/Gradle toolchain in this environment so I couldn't build or run this - I'd appreciate someone testing the actual permission dialog on an API 37 emulator/device before merge. I also haven't tested the LAN end-to-end (a second device actually connecting through the opened proxy), just that the config and permission flow line up.

[bitmold]

Rebased with master and reviewing now...

[bitmold]

@munzzyy Thank you so much for implementing this and for making your first contribution to Orbot! This was a very high quality PR and I'm very grateful for it. ⭐

Normally, I'd ask you to make some changes to this PR and provide feedback, but since we have a release coming out very soon - I made them myself. All of your core logic was solid, but I made the following changes/refactors:

• Used an AlertDialog instead of a Toast when using the open proxy on all interfaces setting. You couldn't see the whole message as a Toast, and it disappears before showing the unfortunately very vague and scary "access nearby devices" system prompt Android 17 uses for local network access
• Unset the preference in Orbot's settings UI if the user revoked it
• Prefs.openProxyOnAllInterfaces now takes a Context and checks for the permission if API 37+. I moved your logic for this from TorConfig to Prefs.
• Moved the now duplicated logic to open Orbot's settings to one place

I'm definitely open to any future improvements around this if you have further suggestions/opinions.

Thanks again for making Orbot better ❤️