feat: add documentation for Overte domain authentication methods and troubleshooting

OVERTE_AUTH.md

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+# Overte Domain Authentication
+
+## Running with Authentication
+
+The Stardust-Overte client now supports domain authentication. Use one of the following methods:
+
+### Method 1: Interactive Script
+```bash
+./run_with_auth.sh
+```
+This will prompt you for username and password.
+
+### Method 2: Environment Variables
+```bash
+OVERTE_USERNAME="your_username" OVERTE_PASSWORD="your_password" ./build/stardust-overte-client
+```
+
+### Method 3: Export Variables
+```bash
+export OVERTE_USERNAME="your_username"
+export OVERTE_PASSWORD="your_password"
+./build/stardust-overte-client
+```
+
+## Configuration
+
+- **OVERTE_USERNAME**: Your Overte domain username
+- **OVERTE_PASSWORD**: Your Overte domain password or access token
+- **OVERTE_UDP_PORT**: Domain server UDP port (default: 40104)
+- **STARWORLD_SIMULATE**: Set to "1" to enable simulation mode with demo entities
+
+## Troubleshooting
+
+If you're not receiving entities:
+
+1. **Check authentication**: Make sure you've set up a user account in the Overte domain web interface (http://localhost:40102/settings/)
+
+2. **Check domain server is running**:
+   ```bash
+   ps aux | grep domain-server
+   sudo ss -ulnp | grep domain-server
+   ```
+
+3. **Test with simulation mode first**:
+   ```bash
+   STARWORLD_SIMULATE=1 ./build/stardust-overte-client
+   ```
+
+4. **Check for connection denied messages** in the output
+
+## Protocol Implementation Status
+
+✅ Domain connection handshake
+✅ Authentication (username/password)
+✅ DomainList request/response
+✅ EntityServer discovery
+✅ EntityQuery packets
+✅ Entity Add/Edit/Erase parsing
+⏳ Full property parsing (position, rotation, dimensions)
+⏳ Octree-based spatial streaming
+⏳ Avatar mixer integration
+⏳ Audio mixer integration