fix(desktop): route fetch + WebSocket through native Tauri plugins (mixed-content)

Fixing VITE_API_BASE got login to build a correct absolute URL, but it still
failed with WebKit's generic "Load failed" — WebKitGTK treats tauri://localhost
as a secure origin, so http://127.0.0.1:3000 (and ws://) from inside it is
blocked as mixed content, a WebKit limitation CSP's connect-src can't override.

Added tauri-plugin-http (genuine fetch() drop-in, wired via a new
platformFetch() in origin.ts, used by api.ts + logger.ts) and
tauri-plugin-websocket (not a drop-in — adapted behind a native-WebSocket-
shaped interface in the new platform-ws.ts so use-live-feed.ts needed no
changes). Both route through Tauri's Rust side instead of the webview's own
fetch/WebSocket. Capabilities scoped to 127.0.0.1:3000/localhost:3000, matching
the existing CSP allowlist.

apps/desktop/src-tauri/src/lib.rs

@@ -16,6 +16,13 @@ pub fn run() {
         // endpoint + signing pubkey live in tauri.conf.json.
         .plugin(tauri_plugin_updater::Builder::new().build())
         .plugin(tauri_plugin_process::init())
+        // Routes the SPA's fetch()/WS calls to the local Fastify server through
+        // Tauri's native HTTP client — see the Cargo.toml comment on why the
+        // webview's own fetch() can't reach http://127.0.0.1:3000 directly.
+        .plugin(tauri_plugin_http::init())
+        // Live-feed WebSocket — same mixed-content reason as the HTTP plugin
+        // above, but WS needs its own plugin (separate browser check).
+        .plugin(tauri_plugin_websocket::init())
         .run(tauri::generate_context!())
         .expect("error while running the Parking System desktop shell");
 }