feat(shared): add platform-specific regex validation for card handles

[mramansayyad]

Summary

Introduces strict platform-specific regex pattern checking on card creation and update payloads to prevent broken hyperlinks on developer cards.

Contexts

The POST /cards and PUT /cards/:id endpoints accept string inputs for usernames and profile URLs. Without platform-level constraints, users can submit formatting errors (e.g., spaces or unsupported special characters in a GitHub or Twitter handle). This results in malformed links on both the mobile interface and web backup layouts.

Tasks

• Define rigid regex verification strings for major platforms (GitHub, Twitter, LinkedIn) within packages/shared/src/platforms.ts.
• Bind validations inside the core zod input payload schemas.
• Attach structured validation messages returning 400 Validation Failed if input criteria are violated.
• Update shared workspace validation tests.

Acceptance Criteria

• Payloads containing illegal characters for specific developer profiles are blocked with a 400 status.
• Well-formatted handles pass validation without any latency or regression.
• Unit tests covering valid/invalid handle boundaries are updated and pass successfully.

Area

shared / backend

Difficulty

Easy

[pari7maheshwari]

hey @mramansayyad I would like to work on this issue under gssoc'26.Can u assign it to me.

[Harxhit]

@mramansayyad I have assigned this issue to you.

[mramansayyad]

Hi @Harxhit, I have fixed the issue #252 and updated the PR #289 with the required changes and test terminal proofs. Kindly review and request to merge. Thanks!