Adds the tag removal migration to the inline migrations in database.py:
- Drops tag-related triggers and functions
- Removes tag_constraint column from artifact_dependencies
- Makes version_constraint NOT NULL
- Drops tags and tag_history tables
- Renames uploads.tag_name to version
- Backend: Python 3.12 with FastAPI, SQLAlchemy, boto3
- Frontend: React 18 with TypeScript, Vite build tooling
- Updated Dockerfile for multi-stage Node + Python build
- Updated CI pipeline for Python backend
- Removed old Go code (cmd/, internal/, go.mod, go.sum)
- Updated README with new tech stack documentation
