Add Wayfinder provider

[Finesssee]

Summary

• add the opt-in Wayfinder gateway provider across Rust, Tauri, CLI, settings, tray cards, and localization
• parse upstream health, model, savings, route, and pricing telemetry without mixing provider identity or quota fields
• restrict gateway configuration to credential-free, fragment-free HTTP loopback URLs and preserve same-origin redirects

Upstream mapping

Ports the Windows-equivalent Wayfinder behavior from upstream CodexBar v0.42.0. macOS-native settings/sidebar presentation is intentionally represented by the existing Windows Tauri provider settings UI.

Validation

• cargo test --manifest-path rust/Cargo.toml (550 + 1 passed)
• cargo test --manifest-path apps/desktop-tauri/src-tauri/Cargo.toml (303 passed)
• cargo clippy --manifest-path rust/Cargo.toml --all-targets -- -D warnings
• cargo clippy --manifest-path apps/desktop-tauri/src-tauri/Cargo.toml --all-targets -- -D warnings
• npm test -- --run (141 passed)
• npm run build
• locale parity: 572 keys
• git diff --check