Implement comprehensive input sanitization

[Naomi-Gift]

Priority: Medium
Type: Security
Description: The utils.rs file has placeholder functions that need implementation:
sanitize_string() currently just clones input - should strip control characters, normalize whitespace
is_valid_category() returns true - should validate against allowed categories or format
is_valid_url() returns true - should validate URL format
is_valid_ipfs_cid() has basic length check - should validate CID format (base58/base32)
Add tests for each validation function

[Oluwasuyi-Timilehin]

@Oluwasuyi-Timilehin has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hello can i work on this?

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[Aonlike]

@Aonlike has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

I would like to work on this issue. I am a Full Stack Developer.

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[veemakama]

@veemakama has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hi maintainer, I'd love to work on this issue.

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[muhahahmad68]

@muhahahmad68 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Kindly assign this to me, I'd like to work on it

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[drips-wave]

Congratulations, @muhahahmad68! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @muhahahmad68: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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