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_osm_config.py

@@ -0,0 +1,28 @@
+from backend.app.core.osm_config import (
+    DEFAULT_REGIONS,
+    STATION_TAG_FILTERS,
+    BoundingBox,
+    compile_overpass_filters,
+)
+
+
+def test_default_regions_are_valid() -> None:
+    assert DEFAULT_REGIONS, "Expected at least one region definition"
+    for bbox in DEFAULT_REGIONS:
+        assert isinstance(bbox, BoundingBox)
+        assert bbox.north > bbox.south
+        assert bbox.east > bbox.west
+        # Berlin coordinates should fall inside Berlin bounding box for sanity
+        if bbox.name == "berlin_metropolitan":
+            assert bbox.contains(52.5200, 13.4050)
+
+
+def test_station_tag_filters_compile_to_overpass_snippet() -> None:
+    compiled = compile_overpass_filters(STATION_TAG_FILTERS)
+    # Ensure each key is present with its values
+    for key, values in STATION_TAG_FILTERS.items():
+        assert key in compiled
+        for value in values:
+            assert value in compiled
+    # The snippet should be multi-line to preserve readability
+    assert "\n" in compiled