Add API endpoints for listing tagged versions and artifacts

- Enhanced GET /api/v1/project/{project}/{package}/tags with pagination,
  search, sort, order parameters and artifact metadata
- Added GET /api/v1/project/{project}/{package}/tags/{tag_name} for
  single tag with full artifact details
- Added GET /api/v1/project/{project}/{package}/tags/{tag_name}/history
  for tag change history
- Added GET /api/v1/project/{project}/{package}/artifacts for listing
  all artifacts in a package with filtering by content_type and date range
- Enhanced GET /api/v1/artifact/{artifact_id} to include list of
  packages/tags referencing the artifact
- Added new schemas: TagDetailResponse, TagHistoryResponse,
  ArtifactDetailResponse, ArtifactTagInfo, PackageArtifactResponse

backend/app/schemas.py

@@ -129,6 +129,78 @@ class TagResponse(BaseModel):
         from_attributes = True
 
 
+class TagDetailResponse(BaseModel):
+    """Tag with embedded artifact metadata"""
+    id: UUID
+    package_id: UUID
+    name: str
+    artifact_id: str
+    created_at: datetime
+    created_by: str
+    # Artifact metadata
+    artifact_size: int
+    artifact_content_type: Optional[str]
+    artifact_original_name: Optional[str]
+    artifact_created_at: datetime
+    artifact_format_metadata: Optional[Dict[str, Any]] = None
+
+    class Config:
+        from_attributes = True
+
+
+class TagHistoryResponse(BaseModel):
+    """History entry for tag changes"""
+    id: UUID
+    tag_id: UUID
+    old_artifact_id: Optional[str]
+    new_artifact_id: str
+    changed_at: datetime
+    changed_by: str
+
+    class Config:
+        from_attributes = True
+
+
+class ArtifactTagInfo(BaseModel):
+    """Tag info for embedding in artifact responses"""
+    id: UUID
+    name: str
+    package_id: UUID
+    package_name: str
+    project_name: str
+
+
+class ArtifactDetailResponse(BaseModel):
+    """Artifact with list of tags/packages referencing it"""
+    id: str
+    size: int
+    content_type: Optional[str]
+    original_name: Optional[str]
+    created_at: datetime
+    created_by: str
+    ref_count: int
+    format_metadata: Optional[Dict[str, Any]] = None
+    tags: List[ArtifactTagInfo] = []
+
+    class Config:
+        from_attributes = True
+
+
+class PackageArtifactResponse(BaseModel):
+    """Artifact with tags for package artifact listing"""
+    id: str
+    size: int
+    content_type: Optional[str]
+    original_name: Optional[str]
+    created_at: datetime
+    created_by: str
+    format_metadata: Optional[Dict[str, Any]] = None
+    tags: List[str] = []  # Tag names pointing to this artifact
+
+    class Config:
+        from_attributes = True
+
+
 # Upload response
 class UploadResponse(BaseModel):
     artifact_id: str