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/postcss/lib/list.js

@@ -0,0 +1,58 @@
+'use strict'
+
+let list = {
+  comma(string) {
+    return list.split(string, [','], true)
+  },
+
+  space(string) {
+    let spaces = [' ', '\n', '\t']
+    return list.split(string, spaces)
+  },
+
+  split(string, separators, last) {
+    let array = []
+    let current = ''
+    let split = false
+
+    let func = 0
+    let inQuote = false
+    let prevQuote = ''
+    let escape = false
+
+    for (let letter of string) {
+      if (escape) {
+        escape = false
+      } else if (letter === '\\') {
+        escape = true
+      } else if (inQuote) {
+        if (letter === prevQuote) {
+          inQuote = false
+        }
+      } else if (letter === '"' || letter === "'") {
+        inQuote = true
+        prevQuote = letter
+      } else if (letter === '(') {
+        func += 1
+      } else if (letter === ')') {
+        if (func > 0) func -= 1
+      } else if (func === 0) {
+        if (separators.includes(letter)) split = true
+      }
+
+      if (split) {
+        if (current !== '') array.push(current.trim())
+        current = ''
+        split = false
+      } else {
+        current += letter
+      }
+    }
+
+    if (last || current !== '') array.push(current.trim())
+    return array
+  }
+}
+
+module.exports = list
+list.default = list