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/node_modules/balanced-match/dist/esm/index.js

@@ -0,0 +1,54 @@
+export const balanced = (a, b, str) => {
+    const ma = a instanceof RegExp ? maybeMatch(a, str) : a;
+    const mb = b instanceof RegExp ? maybeMatch(b, str) : b;
+    const r = ma !== null && mb != null && range(ma, mb, str);
+    return (r && {
+        start: r[0],
+        end: r[1],
+        pre: str.slice(0, r[0]),
+        body: str.slice(r[0] + ma.length, r[1]),
+        post: str.slice(r[1] + mb.length),
+    });
+};
+const maybeMatch = (reg, str) => {
+    const m = str.match(reg);
+    return m ? m[0] : null;
+};
+export const range = (a, b, str) => {
+    let begs, beg, left, right = undefined, result;
+    let ai = str.indexOf(a);
+    let bi = str.indexOf(b, ai + 1);
+    let i = ai;
+    if (ai >= 0 && bi > 0) {
+        if (a === b) {
+            return [ai, bi];
+        }
+        begs = [];
+        left = str.length;
+        while (i >= 0 && !result) {
+            if (i === ai) {
+                begs.push(i);
+                ai = str.indexOf(a, i + 1);
+            }
+            else if (begs.length === 1) {
+                const r = begs.pop();
+                if (r !== undefined)
+                    result = [r, bi];
+            }
+            else {
+                beg = begs.pop();
+                if (beg !== undefined && beg < left) {
+                    left = beg;
+                    right = bi;
+                }
+                bi = str.indexOf(b, i + 1);
+            }
+            i = ai < bi && ai >= 0 ? ai : bi;
+        }
+        if (begs.length && right !== undefined) {
+            result = [left, right];
+        }
+    }
+    return result;
+};
+//# sourceMappingURL=index.js.map