Add unit tests for station service and enhance documentation

- Introduced unit tests for the station service, covering creation, updating, and archiving of stations.
- Added detailed building block view documentation outlining the architecture of the Rail Game system.
- Created runtime view documentation illustrating key user interactions and system behavior.
- Developed concepts documentation detailing domain models, architectural patterns, and security considerations.
- Updated architecture documentation to reference new detailed sections for building block and runtime views.

backend/tests/test_stations_import.py

@@ -0,0 +1,67 @@
+from backend.scripts.stations_import import (
+    build_overpass_query,
+    normalize_station_elements,
+)
+
+
+def test_build_overpass_query_single_region() -> None:
+    query = build_overpass_query("berlin_metropolitan")
+
+    # The query should reference the Berlin bounding box coordinates.
+    assert "52.3381" in query  # south
+    assert "52.6755" in query  # north
+    assert "13.0884" in query  # west
+    assert "13.7611" in query  # east
+    assert "node" in query
+    assert "out body" in query
+
+
+def test_build_overpass_query_all_regions_includes_union() -> None:
+    query = build_overpass_query("all")
+
+    # Ensure multiple regions are present by checking for repeated bbox parentheses.
+    assert query.count("node") >= 3
+    assert query.strip().endswith("out skel qt;")
+
+
+def test_normalize_station_elements_filters_and_transforms() -> None:
+    raw_elements = [
+        {
+            "type": "node",
+            "id": 123,
+            "lat": 52.5,
+            "lon": 13.4,
+            "tags": {
+                "name": "Sample Station",
+                "ref": "XYZ",
+                "ele": "35.5",
+            },
+        },
+        {
+            "type": "node",
+            "id": 999,
+            # Missing coordinates should be ignored
+            "tags": {"name": "Broken"},
+        },
+        {
+            "type": "node",
+            "id": 456,
+            "lat": 50.0,
+            "lon": 8.0,
+            "tags": {
+                "name": "Disused Station",
+                "disused": "yes",
+            },
+        },
+    ]
+
+    stations = normalize_station_elements(raw_elements)
+
+    assert len(stations) == 2
+    primary = stations[0]
+    assert primary["osm_id"] == "123"
+    assert primary["name"] == "Sample Station"
+    assert primary["code"] == "XYZ"
+    assert primary["elevation_m"] == 35.5
+    disused_station = stations[1]
+    assert disused_station["is_active"] is False