Add image and streaming from USB camera

Plus a little freshen up of the readme's

camera_publisher/README.md

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+# Camera Publisher
+
+ROS 2 node that captures frames from a V4L2 USB camera using GStreamer and publishes them as `sensor_msgs/Image` messages.
+
+---
+
+## Architecture
+
+```
+USB Camera → v4l2src (GStreamer) → sensor_msgs/Image → /camera/image_raw
+```
+
+No OpenCV or cv_bridge required. Frames are captured via `v4l2src` and passed directly into the ROS 2 message.
+
+---
+
+## Published topics
+
+| Topic | Type | Description |
+|---|---|---|
+| `/<CAMERA_NAMESPACE>/image_raw` | `sensor_msgs/Image` | Raw camera frames |
+
+---
+
+## Environment variables
+
+| Variable | Default | Description |
+|---|---|---|
+| `VIDEO_DEVICE` | `/dev/video0` | V4L2 device path |
+| `WIDTH` | `640` | Capture width in pixels |
+| `HEIGHT` | `480` | Capture height in pixels |
+| `FPS` | `30` | Capture frame rate |
+| `CAMERA_FORMAT` | `raw` | Capture format (`raw` or `mjpeg`) |
+| `CAMERA_NAMESPACE` | `/camera` | ROS 2 namespace (topic becomes `/<ns>/image_raw`) |
+
+---
+
+## Finding your camera device
+
+```bash
+v4l2-ctl --list-devices
+v4l2-ctl -d /dev/video0 --list-formats-ext
+```