feat: add S3 authentication and fix Docker multi-segment routes

S3 Storage:
- Implement AWS Signature v4 for S3-compatible storage (MinIO, AWS)
- Add s3_access_key, s3_secret_key, s3_region config options
- Support both authenticated and anonymous S3 access
- Add proper URI encoding for S3 canonical requests

Docker Registry:
- Fix routing for multi-segment image names (e.g., library/alpine)
- Add namespace routes for two-segment paths (/v2/{ns}/{name}/...)
- Add debug tracing for upstream proxy operations

Config:
- Add NORA_STORAGE_S3_ACCESS_KEY env var
- Add NORA_STORAGE_S3_SECRET_KEY env var
- Add NORA_STORAGE_S3_REGION env var (default: us-east-1)

nora-registry/src/storage/mod.rs

@@ -59,9 +59,15 @@ impl Storage {
         }
     }
 
-    pub fn new_s3(s3_url: &str, bucket: &str) -> Self {
+    pub fn new_s3(
+        s3_url: &str,
+        bucket: &str,
+        region: &str,
+        access_key: Option<&str>,
+        secret_key: Option<&str>,
+    ) -> Self {
         Self {
-            inner: Arc::new(S3Storage::new(s3_url, bucket)),
+            inner: Arc::new(S3Storage::new(s3_url, bucket, region, access_key, secret_key)),
         }
     }