fix(mining-app): C2C 发布页单价单位改为"绿积分/积分值"

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mining-app/lib/presentation/pages/c2c/c2c_publish_page.dart

@@ -258,7 +258,7 @@ class _C2cPublishPageState extends ConsumerState<C2cPublishPage> {
                   style: TextStyle(fontSize: 16, color: _darkText),
                 ),
                 Text(
-                  '元/积分值 (固定)',
+                  '绿积分/积分值 (固定)',
                   style: TextStyle(color: _grayText, fontSize: 14),
                 ),
               ],