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.showcase.tsx

@@ -0,0 +1,32 @@
+import { View } from "react-native"
+import tw from "twrnc"
+
+import { Button } from "./button"
+import { FeedCard } from "./feed-card"
+import { SansSerifText } from "./sans-serif-text"
+import { SerifText } from "./serif-text"
+import { type Showcase, Section } from "../showcase"
+
+function FeedCardShowcase() {
+	return (
+		<View style={tw`gap-6`}>
+			<Section title="Default">
+				<FeedCard style={tw`p-4`}>
+					<SansSerifText>Card content goes here</SansSerifText>
+				</FeedCard>
+			</Section>
+			<Section title="With mixed content">
+				<FeedCard style={tw`p-4 gap-2`}>
+					<SerifText style={tw`text-xl`}>Title</SerifText>
+					<SansSerifText>Body text inside a feed card.</SansSerifText>
+					<Button style={tw`self-start mt-2`} label="Action" />
+				</FeedCard>
+			</Section>
+		</View>
+	)
+}
+
+export const feedCardShowcase: Showcase = {
+	title: "FeedCard",
+	component: FeedCardShowcase,
+}