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>

apps/aelis-client/src/components/ui/serif-text.tsx

@@ -0,0 +1,10 @@
+import { Text, type TextProps } from "react-native"
+import tw from "twrnc"
+
+export function SerifText({ children, style, ...props }: TextProps) {
+	return (
+		<Text style={[tw`text-stone-800 dark:text-stone-200`, { fontFamily: "Source Serif 4" }, style]} {...props}>
+			{children}
+		</Text>
+	)
+}