feat: Remote registry support and Realizar integration

[noahgift]

Summary

Add remote registry support and Realizar integration for unified model serving.

Spec: ../realizar/docs/specifications/local-global-slm-apr-llm-single-story-spec.md

Deliverables

Registry Backends

• Local SQLite registry (existing)
• Remote S3 backend (s3://bucket/prefix)
• Remote GCS backend (gs://bucket/prefix)
• Hybrid mode (local cache + remote source)

URI Scheme

pacha://model-name:version          # Explicit version
pacha://model-name:latest           # Latest version
pacha://model-name@sha256:abc123    # Content-addressed
pacha://model-name:production       # Stage alias

API Extensions

// Local registry (existing)
let registry = pacha::Registry::local("~/.realizar/models")?;

// Remote registry (NEW)
let registry = pacha::Registry::remote("s3://company-models")?;

// Hybrid (NEW)
let registry = pacha::Registry::hybrid(local, remote)?;

// Stage promotion (NEW)
registry.promote("my-model:1.0.0", Stage::Production)?;

CLI Commands

pacha push model.gguf --name my-model --version 1.0.0
pacha pull pacha://my-model:latest
pacha list [--remote]
pacha promote my-model:1.0.0 --stage production
pacha verify pacha://my-model:production

Model Lifecycle States

[Registered] → [Staged] → [Production] → [Deprecated]

Dependencies

• Realizar: feat: Local-Global Unified Model Serving (ollama/llamafile experience) realizar#20 (consumer)
• Batuta: feat: Add serve/deploy commands for unified model serving batuta#12 (orchestrator)

Toyota Way Alignment

• Kanban: Explicit lifecycle states
• Jidoka: BLAKE3 verification, Ed25519 signing
• Genchi Genbutsu: Model lineage tracking

[noahgift]

Triage: P2. Feature request — remote registry (S3/GCS) with hybrid mode. Well-specified but depends on downstream demand from realizar integration.

[noahgift]

Triage 2026-03-31: Feature request — leave open.