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/@isaacs/cliui/dist/esm/strip-ansi/index.d.ts

@@ -0,0 +1,2 @@
+export declare const stripAnsi: (str: string) => string;
+//# sourceMappingURL=index.d.ts.map

frontend/node_modules/@isaacs/cliui/dist/esm/strip-ansi/index.d.ts.map

@@ -0,0 +1 @@
+{"version":3,"file":"index.d.ts","sourceRoot":"","sources":["../../../src/strip-ansi/index.ts"],"names":[],"mappings":"AAEA,eAAO,MAAM,SAAS,GAAI,KAAK,MAAM,WAA2B,CAAC"}

frontend/node_modules/@isaacs/cliui/dist/esm/strip-ansi/index.js

@@ -0,0 +1,4 @@
+import { ansiRegex } from "../ansi-regex/index.js";
+const regex = ansiRegex();
+export const stripAnsi = (str) => str.replace(regex, "");
+//# sourceMappingURL=index.js.map

frontend/node_modules/@isaacs/cliui/dist/esm/strip-ansi/index.js.map

@@ -0,0 +1 @@
+{"version":3,"file":"index.js","sourceRoot":"","sources":["../../../src/strip-ansi/index.ts"],"names":[],"mappings":"AAAA,OAAO,EAAE,SAAS,EAAE,MAAM,wBAAwB,CAAC;AACnD,MAAM,KAAK,GAAG,SAAS,EAAE,CAAC;AAC1B,MAAM,CAAC,MAAM,SAAS,GAAG,CAAC,GAAW,EAAE,EAAE,CAAC,GAAG,CAAC,OAAO,CAAC,KAAK,EAAE,EAAE,CAAC,CAAC","sourcesContent":["import { ansiRegex } from \"../ansi-regex/index.js\";\nconst regex = ansiRegex();\nexport const stripAnsi = (str: string) => str.replace(regex, \"\");\n"]}