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/storage/mod.rs

@@ -39,6 +39,7 @@ pub type Result<T> = std::result::Result<T, StorageError>;
 pub trait StorageBackend: Send + Sync {
     async fn put(&self, key: &str, data: &[u8]) -> Result<()>;
     async fn get(&self, key: &str) -> Result<Bytes>;
+    async fn delete(&self, key: &str) -> Result<()>;
     async fn list(&self, prefix: &str) -> Vec<String>;
     async fn stat(&self, key: &str) -> Option<FileMeta>;
     async fn health_check(&self) -> bool;
@@ -74,6 +75,11 @@ impl Storage {
         self.inner.get(key).await
     }
 
+    pub async fn delete(&self, key: &str) -> Result<()> {
+        validate_storage_key(key)?;
+        self.inner.delete(key).await
+    }
+
     pub async fn list(&self, prefix: &str) -> Vec<String> {
         // Empty prefix is valid for listing all
         if !prefix.is_empty() && validate_storage_key(prefix).is_err() {