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/showcase.tsx

@@ -0,0 +1,18 @@
+import { View } from "react-native"
+import tw from "twrnc"
+
+import { SansSerifText } from "./ui/sans-serif-text"
+
+export type Showcase = {
+	title: string
+	component: React.ComponentType
+}
+
+export function Section({ title, children }: { title: string; children: React.ReactNode }) {
+	return (
+		<View style={tw`gap-3`}>
+			<SansSerifText style={tw`text-sm text-stone-500 dark:text-stone-400`}>{title}</SansSerifText>
+			{children}
+		</View>
+	)
+}