feat(client): add component library and simplify routing (#66)

* feat(client): add component library and simplify routing

Remove tab layout, explore page, modal, and unused template
components. Replace with single-page layout and a dev component
showcase with per-component detail pages.

- Add Button with label prop, leading/trailing icon support
- Add FeedCard, SerifText, SansSerifText, MonospaceText
- Add colocated *.showcase.tsx files for each component
- Use Stack navigator with themed headers

Co-authored-by: Ona <no-reply@ona.com>

* fix(client): render showcase as JSX component

Co-authored-by: Ona <no-reply@ona.com>

* chore(client): remove dead code chain

Remove ThemedText, useThemeColor, useColorScheme hook,
Colors, and Fonts — none referenced by current screens.

Co-authored-by: Ona <no-reply@ona.com>

---------

Co-authored-by: Ona <no-reply@ona.com>

apps/aelis-client/src/components/ui/feed-card.tsx

@@ -0,0 +1,6 @@
+import { View, type ViewProps } from "react-native"
+import tw from "twrnc"
+
+export function FeedCard({ style, ...props }: ViewProps) {
+	return <View style={[tw`border border-stone-200 dark:border-stone-800 rounded-lg`, style]} {...props} />
+}