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/filelist/index.d.ts

@@ -0,0 +1,110 @@
+// IncludeOptions definitions copied from minimatch (https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/minimatch/index.d.ts)
+interface IncludeOptions {
+  /**
+   * Dump a ton of stuff to stderr.
+   *
+   * @default false
+   */
+  debug?: boolean;
+
+  /**
+   * Do not expand {a,b} and {1..3} brace sets.
+   *
+   * @default false
+   */
+  nobrace?: boolean;
+
+  /**
+   * Disable ** matching against multiple folder names.
+   *
+   * @default false
+   */
+  noglobstar?: boolean;
+
+  /**
+   * Allow patterns to match filenames starting with a period,
+   * even if the pattern does not explicitly have a period in that spot.
+   *
+   * @default false
+   */
+  dot?: boolean;
+
+  /**
+   * Disable "extglob" style patterns like +(a|b).
+   *
+   * @default false
+   */
+  noext?: boolean;
+
+  /**
+   * Perform a case-insensitive match.
+   *
+   * @default false
+   */
+  nocase?: boolean;
+
+  /**
+   * When a match is not found by minimatch.match,
+   * return a list containing the pattern itself if this option is set.
+   * Otherwise, an empty list is returned if there are no matches.
+   *
+   * @default false
+   */
+  nonull?: boolean;
+
+  /**
+   * If set, then patterns without slashes will be matched against
+   * the basename of the path if it contains slashes.
+   *
+   * @default false
+   */
+  matchBase?: boolean;
+
+  /**
+   * Suppress the behavior of treating #
+   * at the start of a pattern as a comment.
+   *
+   * @default false
+   */
+  nocomment?: boolean;
+
+  /**
+   * Suppress the behavior of treating a leading ! character as negation.
+   *
+   * @default false
+   */
+  nonegate?: boolean;
+
+  /**
+   * Returns from negate expressions the same as if they were not negated.
+   * (Ie, true on a hit, false on a miss.)
+   *
+   * @default false
+   */
+  flipNegate?: boolean;
+}
+
+export class FileList {
+  static clone(): FileList
+  static verbose: boolean
+}
+
+export interface FileList extends Omit<Array<string>, "length"> {
+  pendingAdd: string[]
+  pending: boolean
+  excludes: {
+    pats: RegExp[],
+    funcs: Function[],
+    regex: null | RegExp
+  }
+  items: string[]
+  toArray(): string[]
+  include(...items: string[]): this
+  include(...items: (IncludeOptions | string)[]): this
+  exclude(...items: string[]): this
+  shouldExclude(item: string): boolean
+  resolve(): this
+  clearInclusions(): this
+  clearExclusions(): this
+  length(): number
+}