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/web/src/api.ts

@@ -6,7 +6,7 @@
 // wiki/entities/local-jwt-auth.md.
 
 import { logFailedRequest } from "./lib/logger.js";
-import { apiUrl } from "./lib/origin.js";
+import { apiUrl, platformFetch } from "./lib/origin.js";
 import type { AppLogRecord, ValidationLine, ValidationMode } from "@parking/shared";
 
 const CSRF_COOKIE = "parking_csrf";
@@ -28,7 +28,7 @@ export async function apiFetch<T>(path: string, init: RequestInit = {}): Promise
     const csrf = readCookie(CSRF_COOKIE);
     if (csrf) headers.set(CSRF_HEADER, csrf);
   }
-  const res = await fetch(apiUrl(path), { ...init, headers, credentials: "include" });
+  const res = await platformFetch(apiUrl(path), { ...init, headers, credentials: "include" });
   if (!res.ok) {
     const msg = (await res.json().catch(() => ({}))) as { error?: string; problems?: string[]; [k: string]: unknown };
     const error = msg.error ?? `${path}: ${res.status}`;