feat: add context-card diffing utility and validation layer

[Midoriya-w]

Closes #31

Changes:

• Added packages/shared/src/cards.ts with validateCardPlatforms() , diffCardPlatforms() , and CardValidationResult type
• Added packages/shared/src/tests/cards.test.ts 10 test cases covering all edge cases
• Exported from packages/shared/src/index.ts

[Harxhit]

@Midoriya-w Please wait for the issue to be assigned to you before opening a PR. Also, please join our Discord channel from the README section for better communication and project updates.

[Midoriya-w]

Hey @Harxhit! Understood, apologies for jumping ahead I'll wait for assignment before opening PRs going forward. Also the Discord invite link in the README appears to be expired could you share an updated link? Thanks for the assignment and the label!

[Harxhit]

Hey @Harxhit! Understood, apologies for jumping ahead I'll wait for assignment before opening PRs going forward. Also the Discord invite link in the README appears to be expired could you share an updated link? Thanks for the assignment and the label!

Thank you for understanding the process. Here is the discord link: https://discord.gg/E29mKkQt8

[Midoriya-w]

Hey @Harxhit! The shared utility is fully implemented and tested. Regarding backend integration validateCardPlatforms validates platform name strings, but cards.ts uses UUID platformLink references, so direct integration would require schema changes. Happy to add that in a follow-up if needed!