feat: add stop-app script and update desktop shortcut setup

Adds stop-app.sh to kill all services by port (5000-5003, 3000/3001)
and updates setup-desktop-shortcut.sh to create both Start and Stop
desktop shortcuts in a single run. README Step 13 updated accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

stop-app.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+
+# Kill processes by port (backend 5000, selenium 5002, patient extractor 5001, payment OCR 5003, frontend 3000/3001)
+for PORT in 5000 5001 5002 5003 3000 3001; do
+  PIDS=$(lsof -ti :$PORT 2>/dev/null)
+  if [ -n "$PIDS" ]; then
+    echo "Killing port $PORT (PID $PIDS)"
+    kill -9 $PIDS 2>/dev/null
+  fi
+done
+
+# Kill any remaining turbo / ts-node-dev / vite processes for this project
+PROJECT="DentalManagementMH06"
+pkill -9 -f "turbo.*$PROJECT" 2>/dev/null
+pkill -9 -f "ts-node-dev.*$PROJECT" 2>/dev/null
+pkill -9 -f "vite.*$PROJECT" 2>/dev/null
+pkill -9 -f "agent.py" 2>/dev/null
+
+echo "All Dental App processes stopped."