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/terser/main.js

@@ -0,0 +1,27 @@
+import "./lib/transform.js";
+import "./lib/mozilla-ast.js";
+import { minify } from "./lib/minify.js";
+
+export { minify, minify_sync } from "./lib/minify.js";
+export { run_cli as _run_cli } from "./lib/cli.js";
+
+export async function _default_options() {
+    const defs = {};
+
+    Object.keys(infer_options({ 0: 0 })).forEach((component) => {
+        const options = infer_options({
+            [component]: {0: 0}
+        });
+
+        if (options) defs[component] = options;
+    });
+    return defs;
+}
+
+async function infer_options(options) {
+    try {
+        await minify("", options);
+    } catch (error) {
+        return error.defs;
+    }
+}