Add sync error logging, extend error flash, fix unload saves

- Log workforce sync errors to backend stdout so they appear in docker logs
- Extend error flash from 5s to 15s so errors are readable
- Replace sendBeacon (POST-only) with keepalive fetch (PUT) on unload —
  sendBeacon was hitting 404s on all three unload saves

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/hooks/useFrameViewport.js

@@ -0,0 +1,18 @@
+import { useEffect } from 'react';
+const DESKTOP = 'width=1280';
+const RESPONSIVE = 'width=device-width, initial-scale=1.0';
+function setMetaViewport(content) {
+    const meta = document.querySelector('meta[name="viewport"]');
+    if (meta)
+        meta.content = content;
+}
+export function useFrameViewport(mode) {
+    useEffect(() => {
+        setMetaViewport(mode === 'desktop' ? DESKTOP : RESPONSIVE);
+        window.parent.postMessage({ type: 'hnf:viewport', mode }, '*');
+        return () => {
+            setMetaViewport(RESPONSIVE);
+            window.parent.postMessage({ type: 'hnf:viewport', mode: 'responsive' }, '*');
+        };
+    }, [mode]);
+}

frontend/src/hooks/useVersionCheck.js

@@ -0,0 +1,40 @@
+import { useEffect, useState } from 'react';
+const POLL_MS = 2 * 60 * 1000;
+export function useVersionCheck(healthUrl) {
+    const [updateAvailable, setUpdateAvailable] = useState(false);
+    useEffect(() => {
+        let seenVersion = null;
+        async function check() {
+            try {
+                const res = await fetch(healthUrl, { cache: 'no-store' });
+                if (!res.ok)
+                    return;
+                const data = await res.json();
+                const v = data.version;
+                if (!v)
+                    return;
+                if (seenVersion === null) {
+                    seenVersion = v;
+                }
+                else if (v !== seenVersion) {
+                    setUpdateAvailable(true);
+                }
+            }
+            catch {
+                // network error — skip silently
+            }
+        }
+        check();
+        const interval = setInterval(check, POLL_MS);
+        function onVisible() {
+            if (document.visibilityState === 'visible')
+                check();
+        }
+        document.addEventListener('visibilitychange', onVisible);
+        return () => {
+            clearInterval(interval);
+            document.removeEventListener('visibilitychange', onVisible);
+        };
+    }, [healthUrl]);
+    return updateAvailable;
+}