Initial commit: Busbar Designer

Web tool for designing nickel/copper busbars over cylindrical-cell battery
packs (21700, 18650) in hex holders. Flask + build123d backend exports
STEP/DXF/SVG; vanilla JS frontend with live preview, multi-project SQLite
persistence, snapshot history.

Deploy scripts in deploy/ (proxmox-lxc.sh, install.sh, update.sh).

.dockerignore

@@ -0,0 +1,11 @@
+.venv/
+__pycache__/
+*.pyc
+.pytest_cache/
+tests/
+*.md
+.git/
+.gitignore
+data/
+.vscode/
+.idea/