feat: add native Share action for resource URL

[Sughter99]

Closes #7

What this PR does

Adds a native Share button to ResourceCard that opens the iOS/Android
share sheet with the resource title and URL.

Changes

• Updated src/components/ResourceCard.tsx
  • Added handleShare() using React Native's built-in Share API
  • Share content includes resource title + accessUrl
  • message field used on Android (plain text)
  • url field used on iOS (URL sharing path in share sheet)
  • Added Share button next to existing Copy URL button

Acceptance Criteria

• Uses native share sheet (iOS/Android) via React Native Share API
• Shared content includes resource title + URL

Notes

No extra packages needed — React Native's Share API is built into
Expo 52 and works on both iOS and Android natively.

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