Wire Share My Connection toggle in Dart UI (PR 4/4)

[myleshorton]

Final PR in the four-PR client-side stack for Share My Connection. Stacks on #8729 (FFI exports); base = `fisk/peer-ffi`. Re-target to `main` after #8729 merges.

Combined with the rest of the stack — radiance #458 / #460 and lantern-cloud #2678–#2681 — this ships a feature-complete Phase 1 for desktop (macOS + Linux + Windows).

End-to-end flow

```
Dart toggle → RadianceSettings.setPeerProxy(bool)
→ LanternService.setPeerProxyEnabled
→ FFI: setPeerProxyEnabled(int) -> *char
→ LanternCore.SetPeerShareEnabled(bool)
→ ipc.Client.PatchSettings({PeerShareEnabledKey: ...})
→ radiance LocalBackend.PatchSettings dispatch
→ peer.Client.Start / Stop
→ UPnP MapPort + register + sing-box samizdat + heartbeat
```

What's in here (152 LOC, 9 files)

• `lantern_generated_bindings.dart` — adds `setPeerProxyEnabled` + `isPeerProxyEnabled` declarations. Note: these were inserted manually rather than via a local `make ffigen` run. The committed bindings are generated from `bin/windows-amd64/liblantern.h` (in CI); regenerating from a local macOS header drops ~5K lines of Windows-only stubs (`__va_start`, `__security_init_cookie`, etc.) that we want to keep. The two new declarations match the existing `setBlockAdsEnabled` shape exactly.
• `LanternCoreService` / `LanternFFIService` / `LanternPlatformService` / `LanternService` — `setPeerProxyEnabled` + `isPeerProxyEnabled` across all four service layers, mirroring `setBlockAdsEnabled`. FFI path on `isFFISupported` platforms (Windows + Linux); MethodChannel fallback on macOS / mobile.
• `RadianceSettingsState` — new `peerProxy` bool field; `copyWith` and equality updated.
• `RadianceSettings` notifier — `setPeerProxy` method using the existing pessimistic pattern (call FFI → log on failure → update state on success), matching `setBlockAds`. `_refresh` now fetches `peerProxy` alongside the others.
• `vpn_setting.dart` — SwitchButton tile gated to `PlatformUtils.isDesktop`, with i18n strings `share_my_connection` and `share_my_connection_subtitle` in `en.po`. Other locales will pick up via the normal translation flow.

Tests

`flutter analyze` clean across all changed files.

Out of scope (Phase 2+)

• Status indicator below the toggle (e.g. "Sharing on <external_ip>:<port>") — radiance already exposes `/peer/status` and `/peer/status/events` SSE in Write a complete spec of Lantern in preparation for a security audit #460, so this is a small follow-up.
• iOS / Android — UPnP doesn't apply on cellular; tablet-class devices behind home NAT could be a follow-up.
• Native MethodChannel handlers for non-FFI platforms (macOS via Swift, etc.) — the toggle works on Windows + Linux out of the box; macOS will need a Swift handler before the toggle does anything (currently the call would fail silently with a `MissingPluginException`).

Test plan

• `flutter analyze`
• Manual end-to-end on a UPnP-capable network: flip toggle → watch radiance logs for `peer client started` → watch lantern-cloud staging for `peerRegister` succeeded → second client routes through advertised port → flip off → `peer client stopped` + row deprecated server-side.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR wires the new “Share My Connection” / peer-proxy preference through the Dart client so the UI can read and toggle the underlying native setting, extending the existing radiance-backed settings flow.

Changes:

• Added setPeerProxyEnabled / isPeerProxyEnabled across the Dart service stack (LanternCoreService, service router, FFI service, platform service, generated bindings).
• Extended RadianceSettingsState and RadianceSettings provider to fetch, store, and mutate the new peerProxy preference.
• Added a desktop-only VPN settings tile plus English locale strings for the new toggle.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
lib/lantern/lantern_service.dart	Routes peer-proxy calls to FFI or platform services.
lib/lantern/lantern_platform_service.dart	Adds MethodChannel-based peer-proxy getters/setters.
lib/lantern/lantern_generated_bindings.dart	Declares the new FFI exports in generated bindings.
lib/lantern/lantern_ffi_service.dart	Wraps the new FFI peer-proxy APIs for Dart callers.
lib/lantern/lantern_core_service.dart	Extends the core service interface with peer-proxy methods.
lib/features/setting/vpn_setting.dart	Adds the Share My Connection toggle to the VPN settings UI.
lib/features/home/provider/radiance_settings_providers.dart	Fetches and updates peer-proxy state in the radiance settings notifier.
lib/core/models/radiance_settings_state.dart	Stores peer-proxy in immutable settings state and equality/hash logic.
assets/locales/en.po	Adds English strings for the new settings tile.

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