Add llama-server and open-webui apps for local LLM inference

- llama-server: llama.cpp REST API server, 8G memory, port 8080
- open-webui: Chat UI connecting to llama-server, 2G memory, port 3000
- Both include x-casaos metadata for ZimaOS app store
- README with model download instructions and API examples

Apps/open-webui/README.md

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+# OpenWebUI
+
+Modern chat web interface for local LLMs. Connects to llama-server via Docker internal networking.
+
+## Purpose
+
+- **Port**: 3000 (TCP)
+- **Memory**: 2G reservation
+- **Category**: AI / LLM UI
+
+Requires the **llama-server** app to be running first. Connects to `http://llama-server:8080` internally.
+
+## Prerequisites
+
+1. Deploy and start **llama-server** app first
+2. Download a GGUF model into llama-server's `/models` directory
+3. Ensure llama-server container is healthy
+
+## Access
+
+Open in browser:
+
+```
+http://<your-zimaos-host>:3000
+```
+
+First run may take a moment to initialize.
+
+## Environment Variables
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `OLLAMA_BASE_URL` | `http://llama-server:8080` | Internal URL to llama-server API |
+| `WEBUI_PORT` | `3000` | Container listen port |
+| `TZ` | `Europe/Stockholm` | Timezone |
+
+## If Connection Fails
+
+1. Verify llama-server is running: `docker ps | grep llama-server`
+2. Check llama-server logs: `docker logs llama-server`
+3. Ensure llama-server MODEL env matches your downloaded file
+4. From ZimaOS shell, test connectivity:
+   ```bash
+   curl http://llama-server:8080/v1/models
+   ```
+
+## Volumes
+
+| Path | Description |
+|------|-------------|
+| `/app/backend/data` | OpenWebUI persistent data (chat history, settings) |
+
+## Architecture
+
+- `amd64` (Intel/AMD x86_64)
+- `arm64` (Apple Silicon, ARM servers)
+
+## Security
+
+- `security_opt: no-new-privileges:true`
+- `cap_drop: ALL`
+
+## Troubleshooting
+
+**"Cannot connect to LLM" error in UI**
+- Verify llama-server is running before open-webui
+- Check that `OLLAMA_BASE_URL` is set to `http://llama-server:8080`
+- Verify model file exists in `/DATA/AppData/llama-server/models/`
+
+**Slow responses**
+- 7B models on CPU are limited by single-thread performance
+- 3B models recommended for interactive speeds (~15+ tok/s)
+- Close other apps to free RAM