feat: nora mirror v0.4 — yarn.lock, --json, Docker images (#94)

* feat: add yarn.lock support and --json output for nora mirror (#43, #44)

- Add yarn.lock v1 parser with scoped packages, multiple ranges, dedup
- Add --json flag for machine-readable mirror output (CI pipelines)
- Add MirrorFormat::Yarn variant
- MirrorResult now implements Serialize
- 12 new tests (10 yarn.lock + 2 json serialization)

Closes #43, closes #44

* feat: add Docker image mirroring (nora mirror docker) (#41)

Add nora mirror docker command to fetch images from upstream registries
(Docker Hub, ghcr.io, etc.) and push them into NORA. Supports:
- Image references: name:tag, name@digest, registry/name:tag
- --images (comma-separated) and --images-file (one per line)
- Manifest list resolution (picks linux/amd64)
- Layer dedup via HEAD check before fetch
- Monolithic blob upload to NORA

Makes fetch_blob_from_upstream and fetch_manifest_from_upstream pub in
registry/docker.rs for reuse from mirror module.

20 new unit tests for image ref parsing, manifest detection, blob extraction.

nora-registry/src/registry/docker.rs

@@ -990,7 +990,7 @@ async fn delete_blob_ns(
 }
 
 /// Fetch a blob from an upstream Docker registry
-async fn fetch_blob_from_upstream(
+pub async fn fetch_blob_from_upstream(
     client: &reqwest::Client,
     upstream_url: &str,
     name: &str,
@@ -1047,7 +1047,7 @@ async fn fetch_blob_from_upstream(
 
 /// Fetch a manifest from an upstream Docker registry
 /// Returns (manifest_bytes, content_type)
-async fn fetch_manifest_from_upstream(
+pub async fn fetch_manifest_from_upstream(
     client: &reqwest::Client,
     upstream_url: &str,
     name: &str,