Rewrote Crabstero from Java to Python.

- Replaced Javacord with discord.py.
- Replaced Redis backend with SQLite via aiosqlite.
- Replaced Gradle build with pyproject.toml and uv.
- Added setuptools-scm for automatic versioning from git tags.
- Added argparse CLI with systemd credential support for the bot token.
- Replaced per-channel ingestion tasks with a bounded queue and worker pool.
- Removed Dockerfile and Gitea Actions workflow.

.gitignore

@@ -1,2 +1,10 @@
-.gradle/
-.idea/
+__pycache__/
+*.pyc
+*.pyo
+*.egg-info/
+dist/
+build/
+.env
+*.db
+.venv/
+crabstero/_version.py