frontend: runtime backend URL (LAN), voice dictation, version + update UI

Resolve the backend URL from the current host at runtime (lib/backend-url.ts)
so one build works on localhost and any clinic LAN IP without a rebuild; used
by the API client, auth client, and socket. Wire the AI-chat mic to the Web
Speech API with graceful fallback. Add a Settings "About & updates" panel
(current/latest version, update command, shareable network address) and an
optional dismissible update banner.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/lib/api-client.ts

@@ -1,8 +1,11 @@
 // Thin fetch wrapper for the temetro backend's non-auth API (patients, …).
 // Auth itself goes through the Better Auth client (lib/auth-client.ts).
 
-export const API_BASE_URL =
-  process.env.NEXT_PUBLIC_API_URL ?? "http://localhost:4000";
+import { resolveBackendUrl } from "@/lib/backend-url";
+
+// Derived from the current host in the browser (see lib/backend-url.ts), so the
+// app works over localhost and the clinic LAN without a per-deployment rebuild.
+export const API_BASE_URL = resolveBackendUrl();
 
 export class ApiError extends Error {
   constructor(