feat: Initial implementation of FitTrack Report Generator

This commit introduces the initial version of the FitTrack Report Generator, a FastAPI application for analyzing workout files.

Key features include:
- Parsing of FIT, TCX, and GPX workout files.
- Analysis of power, heart rate, speed, and elevation data.
- Generation of summary reports and charts.
- REST API for single and batch workout analysis.

The project structure has been set up with a `src` directory for core logic, an `api` directory for the FastAPI application, and a `tests` directory for unit, integration, and contract tests.

The development workflow is configured to use Docker and modern Python tooling.

tests/unit/test_gpx_parser.py

@@ -0,0 +1,58 @@
+import pytest
+from unittest.mock import MagicMock, patch, mock_open
+from src.core.file_parser import GpxParser, WorkoutData, WorkoutMetadata
+from datetime import datetime, timedelta
+
+@pytest.fixture
+def mock_gpxpy_parse():
+    with patch('gpxpy.parse') as mock_parse:
+        mock_gpx = MagicMock()
+        mock_parse.return_value = mock_gpx
+
+        # Mock GPX data
+        mock_gpx.time = datetime(2023, 1, 1, 10, 0, 0)
+        mock_gpx.get_moving_data.return_value.moving_time = 3600
+
+        mock_point1 = MagicMock()
+        mock_point1.time = datetime(2023, 1, 1, 10, 0, 0)
+        mock_point1.latitude = 40.0
+        mock_point1.longitude = -105.0
+        mock_point1.elevation = 1600.0
+
+        mock_point2 = MagicMock()
+        mock_point2.time = datetime(2023, 1, 1, 10, 1, 0)
+        mock_point2.latitude = 40.1
+        mock_point2.longitude = -105.1
+        mock_point2.elevation = 1610.0
+
+        mock_segment = MagicMock()
+        mock_segment.points = [mock_point1, mock_point2]
+
+        mock_track = MagicMock()
+        mock_track.segments = [mock_segment]
+
+        mock_gpx.tracks = [mock_track]
+
+        yield mock_parse
+
+def test_gpx_parser_initialization():
+    parser = GpxParser("dummy.gpx")
+    assert parser.file_path == "dummy.gpx"
+
+def test_gpx_parser_parse_method_returns_workout_data(mock_gpxpy_parse):
+    # Mock the open function as well, since GpxParser directly opens the file
+    with patch('builtins.open', mock_open(read_data="<gpx></gpx>")):
+        parser = GpxParser("dummy.gpx")
+        workout_data = parser.parse()
+
+        mock_gpxpy_parse.assert_called_once() # gpxpy.parse is called
+
+        assert isinstance(workout_data, WorkoutData)
+        assert isinstance(workout_data.metadata, WorkoutMetadata)
+        assert workout_data.metadata.file_type == "GPX"
+        assert workout_data.metadata.start_time == datetime(2023, 1, 1, 10, 0, 0)
+        assert workout_data.metadata.duration == timedelta(seconds=3600)
+        assert not workout_data.time_series_data.empty
+        assert "latitude" in workout_data.time_series_data.columns
+        assert "longitude" in workout_data.time_series_data.columns
+        assert "elevation" in workout_data.time_series_data.columns