feat: scaffold API, commands and tests

[velocitysystems]

Summary

Scaffolds the API contract for cross-platform network connectivity detection: Tauri commands, TypeScript bindings, types, permissions, and stub Rust implementation.

API design informed by platform-native connectivity APIs — Windows NetworkInformation, iOS NWPathMonitor, and Android ConnectivityManager — unified into a single ConnectionStatus model.

Architecture

ConnectionStatus combines reachability, cost/constraint flags, and physical transport type into a single query result:

• connected: bool — whether the device has an active internet connection
• metered: bool — whether data usage is billed or limited (maps to NetworkCostType on Windows, NWPath.isExpensive on iOS, NET_CAPABILITY_NOT_METERED on Android)
• constrained: bool — whether the connection is data-constrained or restricted (maps to ApproachingDataLimit/OverDataLimit/Roaming on Windows, NWPath.isConstrained on iOS, Data Saver on Android)
• connectionType: ConnectionType — the preferred physical transport (wifi, ethernet, cellular, unknown)

ConnectivityExt trait provides Rust-side access via app.connectivity().connection_status() from any Tauri manager type. Uses managed state via .setup() — required for the mobile plugin bridge (PluginApi) when iOS/Android implementations are added.

Platform stub (src/platform.rs) returns Error::Unsupported until platform-specific implementations are added behind #[cfg] gates.

Design decisions

• connected as a status field, not an error — iOS and Android surface "disconnected" as a normal path status, not an exception. Treating it as a field keeps the consumer code path uniform.
• Single connectionType — when multiple interfaces are active (e.g. WiFi + Cellular), this represents the OS-determined preferred transport. Sufficient for network policy decisions without over-complicating the API.
• Error::Unsupported only — platform-specific error variants (PluginInvoke, Windows(...)) will be added via #[cfg] + #[from] when implementations land. Matches the Tauri plugin ecosystem pattern.

Test plan

• npm run standards passes (eslint, tsc, markdownlint, clippy, rustfmt, commitlint, check-node-version)
• npm test passes (7 TypeScript + 7 Rust tests)
• Serde roundtrip tested for all ConnectionType variants and ConnectionStatus
• Error display and serialization tested
• ConnectionStatus::disconnected() convenience constructor tested
• TypeScript IPC mock tests cover wifi, cellular, ethernet, disconnected, and constrained scenarios
• TypeScript error rejection tested

[velocitysystems]

Thanks @jjhafer. All remaining comments have been resolved.