Revert "調整暖色系為鮮明純色"

This reverts commit dc137e33ca.

scripts/check_observability_ui.py

@@ -97,15 +97,14 @@ REQUIRED_SHELL_SNIPPETS = [
     "momo-nav-subtitle",
     "momo-nav-sublink",
     "rgba(255, 248, 238, 0.72)",
-    "background: #f2eadf",
-    "var(--momo-page-accent, #e4573d)",
+    "linear-gradient(180deg",
 ]
 
 FORBIDDEN_SHELL_PATTERNS = [
     Rule(
         "pure_black_sidebar",
         re.compile(r"\.momo-sidebar\s*\{[^}]*background\s*:\s*(#000|black)\b", re.IGNORECASE | re.DOTALL),
-        "側欄不得回退成純黑背景；必須維持暖色系新版 shell。",
+        "側欄不得回退成純黑背景；必須維持暖深咖啡漸層。",
     ),
     Rule(
         "low_contrast_sublink",