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).

.gitattributes

@@ -0,0 +1,22 @@
+# Force LF for shell scripts and systemd units so they work after checkout on Linux,
+# regardless of the developer's core.autocrlf setting.
+*.sh           text eol=lf
+*.service      text eol=lf
+Dockerfile     text eol=lf
+docker-compose.yml text eol=lf
+
+# Normalise line endings on commit, but keep CRLF on Windows checkout for everything else.
+*.py           text
+*.js           text
+*.html         text
+*.css          text
+*.md           text
+*.scad         text
+*.txt          text
+
+# Binary
+*.png binary
+*.jpg binary
+*.stl binary
+*.step binary
+*.dxf binary