feat: add Docker image metadata support

- Store metadata (.meta.json) alongside manifests with:
  - push_timestamp, last_pulled, downloads counter
  - size_bytes, os, arch, variant
  - layers list with digest and size
- Update metadata on manifest pull (increment downloads, update last_pulled)
- Extract OS/arch from config blob on push
- Extend UI API TagInfo with metadata fields
- Add public_url config option for pull commands
- Add Docker upstream proxy with auth support
- Add raw repository support
- Bump version to 0.2.12

nora-registry/src/registry/mod.rs

@@ -1,11 +1,15 @@
 mod cargo_registry;
-mod docker;
+pub mod docker;
+pub mod docker_auth;
 mod maven;
 mod npm;
 mod pypi;
+mod raw;
 
 pub use cargo_registry::routes as cargo_routes;
 pub use docker::routes as docker_routes;
+pub use docker_auth::DockerAuth;
 pub use maven::routes as maven_routes;
 pub use npm::routes as npm_routes;
 pub use pypi::routes as pypi_routes;
+pub use raw::routes as raw_routes;