Add MJPEG camera server with systemd deployment

- camera/capture.py: V4L2 mmap-based MJPEG frame capture with background thread
- camera/mjpeg.py: MJPEG streaming server (multipart/x-mixed-replace) + minimal web UI
- camera/app.py: Entry point with argument parsing and signal handling
- pyproject.toml: uv project config (no external dependencies)
- camera-webui.service: systemd unit for native Pi deployment
- README.md: Updated for systemd-only direction with install instructions

pyproject.toml

@@ -0,0 +1,13 @@
+[project]
+name = "usb-camera-webui"
+version = "0.1.0"
+description = "Live MJPEG video feed from a USB webcam, served via a minimal web UI"
+requires-python = ">=3.11"
+dependencies = []
+
+[project.scripts]
+camera-webui = "camera.app:main"
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"