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/main.rs

@@ -100,6 +100,9 @@ enum Commands {
         /// Max concurrent downloads
         #[arg(long, default_value = "8", global = true)]
         concurrency: usize,
+        /// Output results as JSON (for CI pipelines)
+        #[arg(long, global = true)]
+        json: bool,
     },
 }
 
@@ -188,8 +191,9 @@ async fn main() {
             format,
             registry,
             concurrency,
+            json,
         }) => {
-            if let Err(e) = mirror::run_mirror(format, &registry, concurrency).await {
+            if let Err(e) = mirror::run_mirror(format, &registry, concurrency, json).await {
                 error!("Mirror failed: {}", e);
                 std::process::exit(1);
             }