fix(dev): vite proxy to 127.0.0.1 + throttle error notifications

The dev proxy targeted 'localhost', which Node can resolve to IPv6 ::1 that the
Docker publish doesn't answer after a container recreate — every /api call failed,
spamming 'Network error'. Pin the proxy to 127.0.0.1. Also collapse bursts of
connection/5xx failures into one notification per 30s so a brief restart no longer
floods the notification center.

frontend/src/lib/api.ts

@@ -68,6 +68,16 @@ class HttpError extends Error {
   }
 }
 
+// Collapse bursts of connection failures (e.g. while the server restarts) into a
+// single notification rather than one per failed request.
+let lastErrorNotifiedAt = 0;
+function notifyErrorThrottled(title: string, message: string): void {
+  const now = Date.now();
+  if (now - lastErrorNotifiedAt < 30_000) return;
+  lastErrorNotifiedAt = now;
+  notify({ level: "error", title, message });
+}
+
 async function req(url: string, opts: RequestInit = {}): Promise<any> {
   const method = opts.method ?? "GET";
   let r: Response;
@@ -78,22 +88,16 @@ async function req(url: string, opts: RequestInit = {}): Promise<any> {
       ...opts,
     });
   } catch (e) {
-    // Network/connection failure — surface it in the notification center.
-    notify({
-      level: "error",
-      title: "Network error",
-      message: `Couldn't reach the server (${method} ${url}).`,
-    });
+    notifyErrorThrottled(
+      "Connection lost",
+      "Couldn't reach the server — it may be restarting. This will clear once it's back."
+    );
     throw e;
   }
   if (!r.ok) {
-    // Server faults are worth logging; 401/403/404 etc. are handled by callers.
+    // Server faults are worth surfacing; 401/403/404 etc. are handled by callers.
     if (r.status >= 500) {
-      notify({
-        level: "error",
-        title: `Server error ${r.status}`,
-        message: `${method} ${url}`,
-      });
+      notifyErrorThrottled(`Server error ${r.status}`, `${method} ${url}`);
     }
     throw new HttpError(r.status);
   }

frontend/vite.config.ts

@@ -2,10 +2,13 @@ import { defineConfig } from "vite";
 import react from "@vitejs/plugin-react";
 
 // During `vite dev` (host with Node), proxy API calls to the backend container.
+// Use 127.0.0.1 (not "localhost") so Node doesn't resolve to IPv6 ::1, which the
+// Docker port publish may not answer — that surfaces as proxy connection failures.
+const target = "http://127.0.0.1:8080";
 const proxy = {
-  "/api": "http://localhost:8080",
-  "/auth": "http://localhost:8080",
-  "/healthz": "http://localhost:8080",
+  "/api": target,
+  "/auth": target,
+  "/healthz": target,
 };
 
 export default defineConfig({