Organize markdown files into docs folder and move ErrorFallback component

Co-authored-by: johndoe6345789 <224850594+johndoe6345789@users.noreply.github.com>

docs/QUICKSTART.md

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+# Quick Start Guide
+
+## Choose Your Setup
+
+### 🚀 Full Stack with Docker (Easiest)
+
+Everything runs in Docker with automatic backend configuration.
+
+```bash
+docker-compose up -d
+```
+
+✅ Frontend: http://localhost:3000  
+✅ Backend: http://localhost:5000  
+✅ Auto-configured to use Flask backend
+
+---
+
+### 💻 Local Development
+
+Backend in Docker, frontend in development mode.
+
+```bash
+# Terminal 1: Start backend
+docker-compose -f docker-compose.backend-only.yml up -d
+
+# Terminal 2: Configure and start frontend
+echo "VITE_FLASK_BACKEND_URL=http://localhost:5000" > .env
+npm install
+npm run dev
+```
+
+✅ Frontend: http://localhost:5173 (Vite dev server)  
+✅ Backend: http://localhost:5000  
+✅ Auto-configured to use Flask backend
+
+---
+
+### 🌐 Frontend Only (Local Storage)
+
+No backend required - uses browser IndexedDB.
+
+```bash
+npm install
+npm run dev
+```
+
+✅ Frontend: http://localhost:5173  
+✅ Data stored locally in browser  
+✅ No server needed
+
+---
+
+### ⚙️ Backend Only
+
+Run backend separately, configure frontend manually.
+
+```bash
+cd backend
+pip install -r requirements.txt
+python app.py
+```
+
+Then in a separate terminal:
+```bash
+npm install
+npm run dev
+```
+
+✅ Backend: http://localhost:5000  
+✅ Frontend: http://localhost:5173  
+⚠️ Must configure backend URL in Settings page
+
+---
+
+## Key Features by Setup
+
+| Feature | Full Stack Docker | Local Dev | Frontend Only | Backend Only |
+|---------|------------------|-----------|---------------|--------------|
+| Auto-configured backend | ✅ | ✅ | ❌ | ❌ |
+| Hot reload | ❌ | ✅ | ✅ | ✅ |
+| Multi-device sync | ✅ | ✅ | ❌ | ✅* |
+| No dependencies | ❌ | ❌ | ✅ | ❌ |
+| Production-ready | ✅ | ❌ | ❌ | ⚠️ |
+
+*Requires manual configuration
+
+---
+
+## Environment Variables
+
+### `VITE_FLASK_BACKEND_URL`
+
+**What it does:**  
+Automatically configures the app to use a Flask backend instead of IndexedDB.
+
+**When set:**
+- App connects to Flask backend on startup
+- Settings page backend selection is disabled
+- Overrides any manual configuration
+
+**Examples:**
+
+Local backend:
+```bash
+VITE_FLASK_BACKEND_URL=http://localhost:5000
+```
+
+Docker internal:
+```bash
+VITE_FLASK_BACKEND_URL=http://backend:5000
+```
+
+Remote backend:
+```bash
+VITE_FLASK_BACKEND_URL=https://api.example.com
+```
+
+**Setup methods:**
+
+`.env` file:
+```bash
+echo "VITE_FLASK_BACKEND_URL=http://localhost:5000" > .env
+```
+
+Docker Compose:
+```yaml
+services:
+  frontend:
+    environment:
+      - VITE_FLASK_BACKEND_URL=http://backend:5000
+```
+
+Docker build:
+```bash
+docker build --build-arg VITE_FLASK_BACKEND_URL=http://api.example.com .
+```
+
+---
+
+## Common Commands
+
+### Docker
+
+```bash
+# Start all services
+docker-compose up -d
+
+# Stop all services
+docker-compose down
+
+# View logs
+docker-compose logs -f
+
+# Rebuild after code changes
+docker-compose up -d --build
+
+# Start backend only
+docker-compose -f docker-compose.backend-only.yml up -d
+```
+
+### NPM
+
+```bash
+# Install dependencies
+npm install
+
+# Development server
+npm run dev
+
+# Production build
+npm run build
+
+# Preview production build
+npm run preview
+```
+
+### Backend (Python)
+
+```bash
+cd backend
+
+# Install dependencies
+pip install -r requirements.txt
+
+# Run server
+python app.py
+
+# Run with custom database path
+DB_PATH=/custom/path/snippets.db python app.py
+```
+
+---
+
+## Troubleshooting
+
+### "Connection failed" in Settings
+
+**Problem:** Can't connect to Flask backend
+
+**Solutions:**
+1. Verify backend is running: `curl http://localhost:5000/health`
+2. Check URL is correct (include `http://`)
+3. Ensure no firewall is blocking port 5000
+4. Check backend logs: `docker-compose logs backend`
+
+### Environment variable not working
+
+**Problem:** `VITE_FLASK_BACKEND_URL` not taking effect
+
+**Solutions:**
+1. Restart dev server after creating/modifying `.env`
+2. Ensure file is named `.env` (not `.env.txt`)
+3. Variable must start with `VITE_`
+4. For production builds: rebuild with `npm run build`
+
+### Settings page is read-only
+
+**This is expected** when `VITE_FLASK_BACKEND_URL` is set.
+
+**To enable manual configuration:**
+1. Remove the variable from `.env`
+2. Restart the application
+
+### Port already in use
+
+**Problem:** "Port 3000 (or 5000) is already in use"
+
+**Solutions:**
+
+Change frontend port:
+```yaml
+# docker-compose.yml
+services:
+  frontend:
+    ports:
+      - "8080:3000"  # Access at http://localhost:8080
+```
+
+Change backend port:
+```yaml
+# docker-compose.yml
+services:
+  backend:
+    ports:
+      - "8000:5000"  # Access at http://localhost:8000
+    environment:
+      - VITE_FLASK_BACKEND_URL=http://backend:5000  # Keep internal port same
+```
+
+Or stop the conflicting service:
+```bash
+# Find process using port
+lsof -i :3000
+
+# Kill process (replace PID)
+kill -9 <PID>
+```
+
+---
+
+## Next Steps
+
+- 📖 [Full documentation](./README-APP.md)
+- 🔧 [Backend configuration guide](./BACKEND-CONFIG.md)
+- 🐳 [Docker examples](./docker-compose.README.md)
+- 🚀 [Backend API docs](./backend/README.md)