build(desktop): add electronbuild.sh — multi-platform installer build

Convenience wrapper around `pnpm build:all` in packages/desktop that
builds installers for mac/win/linux × arm64/x64 and collects the
distributable artifacts into packages/desktop/installers/. Excluded
from rsync deploy by deploy.sh.

electronbuild.sh

@@ -0,0 +1,53 @@
+#!/bin/bash
+# ============================================================
+# Backspace — Electron Installer Build Script
+# ============================================================
+# Builds Electron installers for all platforms/architectures
+# (macOS, Windows, Linux × arm64, x64) and copies the user-
+# distributable artifacts into packages/desktop/installers/.
+#
+# Usage:
+#   ./electronbuild.sh
+# ============================================================
+
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+DESKTOP_DIR="$REPO_ROOT/packages/desktop"
+DIST_DIR="$DESKTOP_DIR/dist-electron"
+INSTALLERS_DIR="$DESKTOP_DIR/installers"
+
+if [ ! -d "$DESKTOP_DIR" ]; then
+  echo "Error: $DESKTOP_DIR not found" >&2
+  exit 1
+fi
+
+echo "==> Building Electron installers (mac/win/linux × arm64/x64)..."
+cd "$DESKTOP_DIR"
+pnpm build:all
+
+echo "==> Copying installers to $INSTALLERS_DIR"
+mkdir -p "$INSTALLERS_DIR"
+rm -f "$INSTALLERS_DIR"/*.dmg \
+      "$INSTALLERS_DIR"/*.exe \
+      "$INSTALLERS_DIR"/*.AppImage \
+      "$INSTALLERS_DIR"/*.deb \
+      "$INSTALLERS_DIR"/*.zip
+
+shopt -s nullglob
+copied=0
+for ext in dmg exe AppImage deb zip; do
+  for f in "$DIST_DIR"/*."$ext"; do
+    cp "$f" "$INSTALLERS_DIR/"
+    copied=$((copied + 1))
+  done
+done
+shopt -u nullglob
+
+if [ "$copied" -eq 0 ]; then
+  echo "Error: no installer artifacts found in $DIST_DIR" >&2
+  exit 1
+fi
+
+echo "==> Done. $copied installer(s) in $INSTALLERS_DIR:"
+ls -lh "$INSTALLERS_DIR" | awk 'NR>1 {printf "    %-40s %s\n", $9, $5}'