docs: add CLAUDE.md with themed-styles convention

Document the useThemedStyles hook as the required way to build
theme-derived StyleSheets, so future work (human or AI) follows it
instead of reintroducing the useTheme + useMemo boilerplate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: kfaracik

CLAUDE.md

@@ -0,0 +1,28 @@
+# Project conventions
+
+## Themed styles — use the `useThemedStyles` hook
+
+Components that build a `StyleSheet` from the theme MUST obtain it via
+[`useThemedStyles`](hooks/useThemedStyles.ts). Do NOT hand-roll the
+`useTheme()` + `useMemo(() => createStyles(theme), [theme])` boilerplate.
+
+```tsx
+// ✅ styles only
+const { styles } = useThemedStyles(createStyles);
+
+// ✅ when the component also reads theme directly (icon colors, insets, etc.)
+const { styles, theme } = useThemedStyles(createStyles);
+
+// ✅ parametric factory — pass extra args after the factory
+const { styles } = useThemedStyles(createStyles, disabled);
+
+// ❌ do not do this
+const { theme } = useTheme();
+const styles = useMemo(() => createStyles(theme), [theme]);
+```
+
+- Keep the `createStyles = (theme: Theme, ...args) => StyleSheet.create({ ... })`
+  factory at the bottom of the file, unchanged — the hook memoizes it.
+- The hook returns `{ styles, theme }`; destructure only what you use.
+- `useTheme()` from [context/ThemeContext](context/ThemeContext.tsx) is still fine
+  for components that need `theme` but build no `StyleSheet`.