Self-contained desktop dev script with worktree isolation

dev:desktop now launches its own Metro on a random port + Electron,
no dependency on a shared :8081. In worktrees, Electron gets a unique
userData path and dock badge so multiple instances run side-by-side.

packages/desktop/scripts/dev.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+DESKTOP_DIR="$(cd "$SCRIPT_DIR/.." && pwd)"
+APP_DIR="$(cd "$DESKTOP_DIR/../app" && pwd)"
+ROOT_DIR="$(cd "$DESKTOP_DIR/../.." && pwd)"
+
+# Build the Electron main process
+npm run build:main
+
+# Get a random available port for Metro
+EXPO_PORT=$("$ROOT_DIR/node_modules/.bin/get-port")
+export EXPO_PORT
+
+echo "══════════════════════════════════════════════════════"
+echo "  Paseo Desktop Dev"
+echo "══════════════════════════════════════════════════════"
+echo "  Metro:     http://localhost:${EXPO_PORT}"
+echo "══════════════════════════════════════════════════════"
+
+# Launch Metro + Electron together, kill both on exit
+"$ROOT_DIR/node_modules/.bin/concurrently" \
+  --kill-others \
+  --names "metro,electron" \
+  --prefix-colors "magenta,cyan" \
+  "cd '$APP_DIR' && npx expo start --port $EXPO_PORT" \
+  "$ROOT_DIR/node_modules/.bin/wait-on tcp:$EXPO_PORT && EXPO_DEV_URL=http://localhost:$EXPO_PORT electron '$DESKTOP_DIR'"