feat: add vCard (.vcf) export support for DevCard profiles

[anshika1179]

Summary

This PR implements Issue #179, adding full vCard (.vcf) export and instant contact-saving support across DevCard's web and mobile applications. It introduces a type-safe vCard 3.0 generation helper in packages/shared to parse and format profile information (full name, pronouns, title, company, bio as a note, email, phone, avatar picture URL, and social profile links). A premium, glassmorphic "Save Contact" button has been integrated into SvelteKit web profiles using dynamic Blob downloads, and a corresponding React Native component utilizing the core Share API with secure base64/text fallbacks has been added to the mobile app for zero-dependency native contact sharing.

Closes #179

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Type of Change

• Bug fix
• New feature
• Refactor (no functional change)
• UI / Design change
• Tests only
• Documentation
• Infrastructure / DevOps
• Security

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What Changed

closes #179

1. Shared Package (packages/shared)

• vcard.ts: Implemented type-safe generateVCard and utility functions to dynamically build valid vCard 3.0 records (using correct CRLF line endings, special character escaping, pronoun inclusion, and social link mapping).
• vcard.test.ts: Added 13 comprehensive unit tests validating single/multi-word names, comma/semicolon/backslash escaping, pronoun formatting, and social link integration.
• index.ts: Exported the shared vCard generator helper.

2. Web App (apps/web)

• SaveContactButton.svelte: Created a premium glassmorphic Svelte 5 component utilizing $props and $state that creates an on-the-fly .vcf download using Blob and URL.createObjectURL.
• +page.svelte: Integrated the "Save Contact" button seamlessly into the public profile view under the bio/headline section.
• index.ts: Exported the new web button component.

3. Mobile App (apps/mobile)

• vcard.ts: Added a custom, lightweight Base64 encoder and helper functions specifically for processing vCard data securely without third-party libraries.
• SaveContactButton.tsx: Created a matching premium dark/glassmorphic action button utilizing the React Native core Share API.
• DevCardViewScreen.tsx: Mounted the new contact saving button directly next to other profile action options.

4. Project Root

• README.md: Updated codebase documentation with mapping specifications, platform features, and vCard compliance details.

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How to Test

1. Run Unit Tests:
   Ensure all shared tests pass cleanly:

   pnpm test