fix(tokens): correct offlineAccent to the proposal's specified #E8879A

WU1's commit invented an arbitrary value for offlineAccent instead of using
the exact hex the proposal's WU1 scope line already specifies. listSurface
and liveGreen were correctly de-literalised from existing theme.dart
literals; offlineAccent has no prior literal, but its value is still not
this file's discretion — the proposal states #E8879A explicitly.

test/tema/pluriwave_tokens_test.dart

@@ -27,8 +27,8 @@ void main() {
       },
     );
 
-    test('dark exposes offlineAccent as a genuinely new colour', () {
-      expect(PluriWaveTokens.dark.offlineAccent, const Color(0xFF94A3B8));
+    test('dark exposes offlineAccent per the proposal (#E8879A)', () {
+      expect(PluriWaveTokens.dark.offlineAccent, const Color(0xFFE8879A));
     });
 
     test('copyWith overrides only the new colour fields', () {