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)

Cargo.toml

@@ -24,3 +24,5 @@ tracing-subscriber = { version = "0.3", features = ["env-filter", "json"] }
 reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"] }
 sha2 = "0.10"
 async-trait = "0.1"
+hmac = "0.12"
+hex = "0.4"