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/strip-comments/lib/Node.js

@@ -0,0 +1,28 @@
+'use strict';
+
+class Node {
+  constructor(node) {
+    this.type = node.type;
+    if (node.value) this.value = node.value;
+    if (node.match) this.match = node.match;
+    this.newline = node.newline || '';
+  }
+  get protected() {
+    return Boolean(this.match) && this.match[1] === '!';
+  }
+}
+
+class Block extends Node {
+  constructor(node) {
+    super(node);
+    this.nodes = node.nodes || [];
+  }
+  push(node) {
+    this.nodes.push(node);
+  }
+  get protected() {
+    return this.nodes.length > 0 && this.nodes[0].protected === true;
+  }
+}
+
+module.exports = { Node, Block };