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).

scad_snippet.scad

@@ -0,0 +1,19 @@
+// Drop this at the END of hex_cell.scad to echo per-cell coordinates
+// in a format the Busbar Designer importer recognises:
+//
+//   ECHO: "Cell 1: x = 0.0, y = 0.0"
+//   ECHO: "Cell 2: x = 22.8, y = 0.0"
+//   ...
+//
+// Origin (0,0) = center of cell at row=0, col=0.
+// Indexing matches the OpenSCAD loop order: row major, then col.
+
+module _echo_cells(centers) {
+    for (i = [0 : len(centers) - 1]) {
+        echo(str("Cell ", i + 1, ": x = ", centers[i].x, ", y = ", centers[i].y));
+    }
+}
+
+if (pack_style == "rect")      _echo_cells(get_hex_center_points_rect(num_rows, num_cols));
+else if (pack_style == "para") _echo_cells(get_hex_center_points_para(num_rows, num_cols));
+else if (pack_style == "tria") _echo_cells(get_hex_center_points_tria(num_rows, num_cols));