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.tsx

@@ -0,0 +1,30 @@
+import { type PressableProps, Pressable, View } from "react-native"
+import tw from "twrnc"
+
+import { SansSerifText } from "./sans-serif-text"
+
+type ButtonProps = Omit<PressableProps, "children"> & {
+	label: string
+	leadingIcon?: React.ReactNode
+	trailingIcon?: React.ReactNode
+}
+
+export function Button({ style, label, leadingIcon, trailingIcon, ...props }: ButtonProps) {
+	const hasIcons = leadingIcon != null || trailingIcon != null
+
+	const textElement = <SansSerifText style={tw`text-stone-200 font-medium`}>{label}</SansSerifText>
+
+	return (
+		<Pressable style={[tw`rounded-full bg-teal-600 px-4 py-3 w-fit`, style]} {...props}>
+			{hasIcons ? (
+				<View style={tw`flex-row items-center gap-1.5`}>
+					{leadingIcon}
+					{textElement}
+					{trailingIcon}
+				</View>
+			) : (
+				textElement
+			)}
+		</Pressable>
+	)
+}