Add a camera feed demo in misc

misc/camera_feed/README.md

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+# Camera Feed Demo
+
+A demo that shows how to display live camera feeds from various sources
+using Godot's [CameraFeed](https://docs.godotengine.org/en/stable/classes/class_camerafeed.html)
+and [CameraServer](https://docs.godotengine.org/en/stable/classes/class_cameraserver.html) APIs.
+Supports multiple platforms including desktop, mobile, and web browsers.
+
+Language: GDScript
+
+Renderer: Compatibility, Mobile, Forward+
+
+> Note: this demo requires Godot 4.5 or later
+
+# How does it work?
+
+The demo uses `CameraServer` to enumerate available camera devices and display their feeds in real-time. Key features include:
+
+1. **Camera Detection**: Automatically detects all available camera feeds using `CameraServer.feeds()`.
+
+2. **Platform Support**:
+   - Handles camera permissions on mobile platforms (Android/iOS)
+   - Supports web browsers with special monitoring setup
+   - Works on desktop platforms with standard camera APIs
+
+3. **Feed Formats**:
+   - RGB format for standard color feeds
+   - YCbCr format with shader-based conversion for certain devices
+   - Dynamic format selection based on camera capabilities
+
+4. **Real-time Display**:
+   - Uses `CameraTexture` to display live camera feeds
+   - Handles camera rotation and orientation transforms
+   - Maintains proper aspect ratio for different camera resolutions
+
+5. **Shader Processing**:
+   - Custom shader (`ycbcr_to_rgb.gdshader`) converts YCbCr feeds to RGB
+   - Uses BT.709 color space conversion standard for HDTV
+
+The UI provides controls to select cameras, choose formats, and start/stop the feed display.
+
+## Screenshots
+
+![Screenshot](screenshots/camera_feed.png)