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).

.gitignore

@@ -0,0 +1,41 @@
+# Python
+__pycache__/
+*.pyc
+*.pyo
+*.pyd
+.Python
+.pytest_cache/
+*.egg-info/
+.coverage
+
+# Virtual env
+.venv/
+venv/
+env/
+
+# Local SQLite DB (lives in deploy target; do not commit project data)
+data/
+tests/_tmp_storage.db
+*.db
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*~
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Build / export artifacts
+*.step
+*.STEP
+*.dxf
+*.DXF
+build/
+dist/
+
+# Local secrets (just in case)
+.env
+.gitea-token