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/unicode-canonical-property-names-ecmascript/index.js

@@ -0,0 +1,60 @@
+module.exports = new Set([
+	// Non-binary properties:
+	'General_Category',
+	'Script',
+	'Script_Extensions',
+	// Binary properties:
+	'Alphabetic',
+	'Any',
+	'ASCII',
+	'ASCII_Hex_Digit',
+	'Assigned',
+	'Bidi_Control',
+	'Bidi_Mirrored',
+	'Case_Ignorable',
+	'Cased',
+	'Changes_When_Casefolded',
+	'Changes_When_Casemapped',
+	'Changes_When_Lowercased',
+	'Changes_When_NFKC_Casefolded',
+	'Changes_When_Titlecased',
+	'Changes_When_Uppercased',
+	'Dash',
+	'Default_Ignorable_Code_Point',
+	'Deprecated',
+	'Diacritic',
+	'Emoji',
+	'Emoji_Component',
+	'Emoji_Modifier',
+	'Emoji_Modifier_Base',
+	'Emoji_Presentation',
+	'Extended_Pictographic',
+	'Extender',
+	'Grapheme_Base',
+	'Grapheme_Extend',
+	'Hex_Digit',
+	'ID_Continue',
+	'ID_Start',
+	'Ideographic',
+	'IDS_Binary_Operator',
+	'IDS_Trinary_Operator',
+	'Join_Control',
+	'Logical_Order_Exception',
+	'Lowercase',
+	'Math',
+	'Noncharacter_Code_Point',
+	'Pattern_Syntax',
+	'Pattern_White_Space',
+	'Quotation_Mark',
+	'Radical',
+	'Regional_Indicator',
+	'Sentence_Terminal',
+	'Soft_Dotted',
+	'Terminal_Punctuation',
+	'Unified_Ideograph',
+	'Uppercase',
+	'Variation_Selector',
+	'White_Space',
+	'XID_Continue',
+	'XID_Start'
+]);