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/estree-walker/README.md

@@ -0,0 +1,48 @@
+# estree-walker
+
+Simple utility for walking an [ESTree](https://github.com/estree/estree)-compliant AST, such as one generated by [acorn](https://github.com/marijnh/acorn).
+
+
+## Installation
+
+```bash
+npm i estree-walker
+```
+
+
+## Usage
+
+```js
+var walk = require( 'estree-walker' ).walk;
+var acorn = require( 'acorn' );
+
+ast = acorn.parse( sourceCode, options ); // https://github.com/acornjs/acorn
+
+walk( ast, {
+  enter: function ( node, parent, prop, index ) {
+    // some code happens
+  },
+  leave: function ( node, parent, prop, index ) {
+  	// some code happens
+  }
+});
+```
+
+Inside the `enter` function, calling `this.skip()` will prevent the node's children being walked, or the `leave` function (which is optional) being called.
+
+Call `this.replace(new_node)` in either `enter` or `leave` to replace the current node with a new one.
+
+Call `this.remove()` in either `enter` or `leave` to remove the current node.
+
+## Why not use estraverse?
+
+The ESTree spec is evolving to accommodate ES6/7. I've had a couple of experiences where [estraverse](https://github.com/estools/estraverse) was unable to handle an AST generated by recent versions of acorn, because it hard-codes visitor keys.
+
+estree-walker, by contrast, simply enumerates a node's properties to find child nodes (and child lists of nodes), and is therefore resistant to spec changes. It's also much smaller. (The performance, if you're wondering, is basically identical.)
+
+None of which should be taken as criticism of estraverse, which has more features and has been battle-tested in many more situations, and for which I'm very grateful.
+
+
+## License
+
+MIT