feat: implement core functionality for camera preview application

- Add FrameDispatcher for distributing QVideoFrames to subscribers
- Implement TelemetryCollector to measure video pipeline performance metrics
- Create MainWindow as the main application interface with video rendering
- Develop AppMenuBar for camera selection, resolution, and FPS settings
- Establish overlay system for displaying telemetry metrics
- Set up project structure and configuration files
- Add unit tests for FrameDispatcher and TelemetryCollector

app/camera/camera_enumerator.py

@@ -0,0 +1,80 @@
+"""Camera enumeration — discovers available video input devices."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+
+from PySide6.QtMultimedia import QCameraDevice, QMediaDevices
+
+
+@dataclass
+class CameraInfo:
+    """Lightweight descriptor of a detected camera."""
+
+    device: QCameraDevice
+    name: str
+    id: str
+    formats: list[tuple[int, int, float]] = field(default_factory=list)
+    # formats: list of (width, height, max_fps)
+
+    def __str__(self) -> str:
+        return f"{self.name} [{self.id}]"
+
+
+class CameraEnumerator:
+    """Discovers available video input devices via QMediaDevices."""
+
+    @staticmethod
+    def list_cameras() -> list[CameraInfo]:
+        """Return all available camera devices with their supported formats."""
+        devices = QMediaDevices.videoInputs()
+        cameras: list[CameraInfo] = []
+
+        for device in devices:
+            formats: list[tuple[int, int, float]] = []
+            for fmt in device.videoFormats():
+                res = fmt.resolution()
+                fps = fmt.maxFrameRate()
+                formats.append((res.width(), res.height(), fps))
+
+            # deduplicate and sort: largest resolution first, then fps descending
+            seen: set[tuple[int, int, float]] = set()
+            unique_formats: list[tuple[int, int, float]] = []
+            for f in sorted(formats, key=lambda x: (x[0] * x[1], x[2]), reverse=True):
+                if f not in seen:
+                    seen.add(f)
+                    unique_formats.append(f)
+
+            cameras.append(
+                CameraInfo(
+                    device=device,
+                    name=device.description(),
+                    id=device.id().toStdString()
+                    if hasattr(device.id(), "toStdString")
+                    else device.id().data().decode("utf-8", errors="replace"),
+                    formats=unique_formats,
+                )
+            )
+
+        return cameras
+
+    @staticmethod
+    def default_camera() -> CameraInfo | None:
+        """Return the system default camera, or None if no camera is available."""
+        device = QMediaDevices.defaultVideoInput()
+        if device.isNull():
+            return None
+
+        cameras = CameraEnumerator.list_cameras()
+        # find by id match
+        default_id = (
+            device.id().toStdString()
+            if hasattr(device.id(), "toStdString")
+            else device.id().data().decode("utf-8", errors="replace")
+        )
+        for cam in cameras:
+            if cam.id == default_id:
+                return cam
+
+        # fallback: wrap directly
+        return cameras[0] if cameras else None