Function process_input 

pub async fn process_input(
    input: &DataInput,
    storage: &dyn StorageTrait,
    hash_algorithm: HashAlgorithm,
    owner_id: Uuid,
    tenant_id: Option<Uuid>,
) -> Result<ProcessedInput, Box<dyn Error>>

Process a single DataInput: resolve URLs, stream to storage, compute content hash, and extract all metadata needed to create a Data record.

This is the first step of the ingest pipeline (Task 1).