Add separate version tracking for artifacts

- Add package_versions table with immutable version records
- Support version detection from explicit param, metadata, or filename
- Add version API endpoints (list, get, delete)
- Update ref resolution to check versions before tags
- Add version column to tags table in frontend UI
- Add Create Tag form for pointing tags at existing artifacts
- Update seed data with version records
- Add 16 integration tests for version functionality

backend/tests/factories.py

@@ -97,6 +97,7 @@ def upload_test_file(
     content: bytes,
     filename: str = "test.bin",
     tag: Optional[str] = None,
+    version: Optional[str] = None,
 ) -> dict:
     """
     Helper function to upload a test file via the API.
@@ -108,6 +109,7 @@ def upload_test_file(
         content: File content as bytes
         filename: Original filename
         tag: Optional tag to assign
+        version: Optional version to assign
 
     Returns:
         The upload response as a dict
@@ -116,6 +118,8 @@ def upload_test_file(
     data = {}
     if tag:
         data["tag"] = tag
+    if version:
+        data["version"] = version
 
     response = client.post(
         f"/api/v1/project/{project}/{package}/upload",