Add GitHub Releases and version-based OTA updates

- Add __version__ = "0.1.0" to src/server.py
- Add release.yml workflow to create GitHub Releases on v* tags
- Refactor start.sh OTA to use GitHub Releases API instead of commit SHAs

src/server.py

@@ -1,4 +1,6 @@
 #!/usr/bin/env python3
+__version__ = "0.1.0"
+
 import asyncio
 import logging
 import os