fix: 修复浅色模式下 text-white 文字不可见，新增主题安全色规范

极速救场标题、个人中心导航和输入框改用语义色

.cursor/rules/project-conventions.mdc

@@ -35,6 +35,13 @@ alwaysApply: true
 - `overflow-y-auto scrollbar-none` for scrollable pages
 - Extract reusable UI patterns into shared components (modals, cards, empty states)
 
+## Theme-Safe Colors
+
+- **Never use `text-white` for content text on page backgrounds** — it becomes invisible in light mode
+- Use semantic colors: `text-heading`, `text-foreground`, `text-secondary`, `text-muted` for content text
+- `text-white` is only correct on **colored backgrounds** (buttons, badges, gradient cards, overlays)
+- Same applies to `bg-black` — prefer `bg-background`, `bg-surface`, `bg-elevated`
+
 ## Loading States
 
 - **Page-level and list-level loading**: always use skeleton screens (`src/components/Skeleton.tsx`), never bare spinners