refactor: update registry type from 'docker-hub' to 'oci' across seed data (#325)

Updates the registry type for all Docker Hub packages in the seed data
from `docker-hub` to `oci` to align with the standardized OCI registry
format. This change affects the `registry_type` field and simplifies the
`identifier` field by removing the full Docker Hub URL prefix.

Changes:
- Updated `registry_type` from `docker-hub` to `oci` for all Docker
packages
- Simplified `identifier` field to use just the repository name/path
instead of full URLs
- Maintained `registry_base_url` as `https://docker.io` for all entries

This refactoring improves consistency and aligns with OCI standards
while maintaining backward compatibility through the registry base URL.

docs/server-json/server.schema.json

@@ -83,8 +83,8 @@
       "properties": {
         "registry_type": {
           "type": "string",
-          "description": "Registry type indicating how to download packages (e.g., 'npm', 'pypi', 'docker-hub', 'nuget', 'mcpb')",
-          "examples": ["npm", "pypi", "docker-hub", "nuget", "mcpb"]
+          "description": "Registry type indicating how to download packages (e.g., 'npm', 'pypi', 'oci', 'nuget', 'mcpb')",
+          "examples": ["npm", "pypi", "oci", "nuget", "mcpb"]
         },
         "registry_base_url": {
           "type": "string",