feat(nip96): native HTTP media storage pipeline

[Ferryx349]

Context & Problem

Nostream relies heavily on fragmented, third-party media servers. Nostream currently acts purely as an event pipeline. Providing a native, integrated media server allows relay operators to offer a complete ecosystem to their users without relying on external services.

Proposed Solution

Build a NIP-96 compliant HTTP upload pipeline directly into Nostream.

Scope

• Auth Integration: Will seamlessly integrate with Nostream's NIP-98 authentication middleware to verify POST signatures.
• Storage Abstraction Layer: Will architect an interface with implementations for Local File System and AWS S3 / Cloudflare R2.
• Ingestion Pipeline: Will use a stream-based parser to handle multipart form data uploads, generate SHA-256 hashes, and enforce mime-type and size limits.
• Response Formatting: will return the standardized NIP-96 JSON response containing the download URL and metadata.

NIPs Involved: NIP-96, NIP-98