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/button.showcase.tsx

@@ -0,0 +1,43 @@
+import Feather from "@expo/vector-icons/Feather"
+import { View } from "react-native"
+import tw from "twrnc"
+
+import { Button } from "./button"
+import { type Showcase, Section } from "../showcase"
+
+function ButtonShowcase() {
+	return (
+		<View style={tw`gap-6`}>
+			<Section title="Default">
+				<Button style={tw`self-start`} label="Press me" />
+			</Section>
+			<Section title="Leading icon">
+				<Button
+					style={tw`self-start`}
+					label="Add item"
+					leadingIcon={<Feather name="plus" size={18} color="#e7e5e4" />}
+				/>
+			</Section>
+			<Section title="Trailing icon">
+				<Button
+					style={tw`self-start`}
+					label="Next"
+					trailingIcon={<Feather name="arrow-right" size={18} color="#e7e5e4" />}
+				/>
+			</Section>
+			<Section title="Both icons">
+				<Button
+					style={tw`self-start`}
+					label="Download"
+					leadingIcon={<Feather name="download" size={18} color="#e7e5e4" />}
+					trailingIcon={<Feather name="chevron-down" size={18} color="#e7e5e4" />}
+				/>
+			</Section>
+		</View>
+	)
+}
+
+export const buttonShowcase: Showcase = {
+	title: "Button",
+	component: ButtonShowcase,
+}