fix(expo-template): render tab bar icons on Android

[oleksandrzavarzin-callstack]

PR Description

Bug fix for @bottom-tabs/expo-template. A scaffolded app had no tab bar icons on Android.

app/(tabs)/_layout.tsx passed only SF Symbols, which are Apple-only. On Android the library
warns once per tab and renders the item with a label and an empty M3 active-indicator pill

• Icons: Platform branch - SF Symbols on iOS, images elsewhere. Ships two 96x96 PNGs.
• Tints: the bar was falling back to React Navigation's colors.primary (the default blue).
  Now uses the template's own Colors.tabIconSelected / tabIconDefault.
• Docs: usage-with-expo-router.mdx mirrored the iOS-only pattern, and imported Tabs from
  @/components/bottom-tabs - a path the guide never tells you to create, so the snippet was
  uncopyable. Fixed both.

How to test?

Pack the template from this branch and scaffold from the tarball:

yarn workspace @bottom-tabs/expo-template pack --out /tmp/expo-template.tgz
npx create-expo-app@latest /tmp/tpl --template /tmp/expo-template.tgz
cd /tmp/tpl && npm run android

• Both tabs show an icon, and the active-indicator pill contains the glyph.
• adb logcat | grep "SF Symbols" is empty (two lines before this PR).
• No LogBox toast on launch.
• Active tab uses #0a7ea4 in light / white in dark; inactive #687076 / #9BA1A6.
• Toggle the system theme at runtime - the bar re-themes correctly.
• On iOS, SF Symbols still render.

Screenshots

Theme	Android	iOS
Light
Dark