[Backend] Add media validation and processing pipeline

[Kaylahray]

Description

The upload route exists, but there is still room for a more complete media pipeline with stronger validation, metadata extraction, and safe handling of user files.

User Story

As a user,
I want to upload media safely,
so that posts and profiles can support rich content without breaking the app.

Requirements and Context

• Files: app/app/api/uploads/route.ts, app/lib/media-utils.ts, app/lib/image-compression.ts, app/lib/file-validation.ts
• Enforce file type, size, and extension validation
• Extract metadata and normalize image uploads consistently
• Return stable upload responses for both post media and avatar use cases

Suggested Implementation

// MEDIA PIPELINE
// 1. Validate file type and size.
// 2. Normalize and compress supported images.
// 3. Store metadata for downstream consumers.
// 4. Reject unsafe or malformed uploads.

Acceptance Criteria

• Invalid file types are rejected before processing.
• Valid media is normalized consistently.
• The upload response is predictable for the frontend.

Submission Guidelines

• Branch: feat/media-processing
• Depends on: upload and media utility modules
• PR: feat(backend): harden media validation and processing

[Danitello123]

@Danitello123 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I’m a smart contract and full-stack developer who turns complex ideas into secure, production-ready blockchain code.
With strong skills in Rust and Solidity, I build systems that are fast, safe, and built to last.
My experience with the Stellar SDK lets me ship real-world Web3 solutions that actually move value

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[KuchiMercy]

@KuchiMercy has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi maintainer, I'd like to work on this issue. Can you assign?

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Congratulations, @KuchiMercy! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

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