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

tests/test_frame_dispatcher.py

@@ -0,0 +1,76 @@
+"""Tests for FrameDispatcher."""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock, patch
+
+from app.pipeline.frame_dispatcher import FrameDispatcher
+
+
+def _make_frame():
+    frame = MagicMock()
+    frame.isValid.return_value = True
+    return frame
+
+
+class TestFrameDispatcher:
+    def setup_method(self):
+        # FrameDispatcher is a QObject — needs QApplication
+        # Use minimal mock to avoid Qt dependency in unit tests
+        with patch("app.pipeline.frame_dispatcher.QObject.__init__", return_value=None):
+            self.dispatcher = FrameDispatcher.__new__(FrameDispatcher)
+            self.dispatcher._subscribers = []
+            self.dispatcher._frame_count = 0
+            self.dispatcher._last_dispatch_time = 0.0
+
+    def test_subscribe_adds_subscriber(self):
+        cb = MagicMock()
+        self.dispatcher.subscribe(cb)
+        assert self.dispatcher.subscriber_count() == 1
+
+    def test_subscribe_same_callback_twice_is_noop(self):
+        cb = MagicMock()
+        self.dispatcher.subscribe(cb)
+        self.dispatcher.subscribe(cb)
+        assert self.dispatcher.subscriber_count() == 1
+
+    def test_unsubscribe_removes_subscriber(self):
+        cb = MagicMock()
+        self.dispatcher.subscribe(cb)
+        self.dispatcher.unsubscribe(cb)
+        assert self.dispatcher.subscriber_count() == 0
+
+    def test_unsubscribe_nonexistent_does_not_raise(self):
+        cb = MagicMock()
+        self.dispatcher.unsubscribe(cb)  # should not raise
+
+    def test_dispatch_calls_all_subscribers(self):
+        cb1 = MagicMock()
+        cb2 = MagicMock()
+        self.dispatcher.subscribe(cb1)
+        self.dispatcher.subscribe(cb2)
+        frame = _make_frame()
+        self.dispatcher.dispatch(frame)
+        cb1.assert_called_once_with(frame)
+        cb2.assert_called_once_with(frame)
+
+    def test_dispatch_increments_frame_count(self):
+        frame = _make_frame()
+        self.dispatcher.dispatch(frame)
+        self.dispatcher.dispatch(frame)
+        assert self.dispatcher.frame_count == 2
+
+    def test_dispatch_with_no_subscribers_does_not_raise(self):
+        frame = _make_frame()
+        self.dispatcher.dispatch(frame)  # should not raise
+
+    def test_subscriber_exception_does_not_stop_others(self):
+        def bad_cb(f):
+            raise RuntimeError("boom")
+
+        good_cb = MagicMock()
+        self.dispatcher.subscribe(bad_cb)
+        self.dispatcher.subscribe(good_cb)
+        frame = _make_frame()
+        self.dispatcher.dispatch(frame)  # should not raise
+        good_cb.assert_called_once_with(frame)