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/app/core/osm_config.py

@@ -0,0 +1,93 @@
+from __future__ import annotations
+
+"""Geographic presets and tagging rules for OpenStreetMap imports."""
+
+from dataclasses import dataclass
+from typing import Iterable, Mapping, Tuple
+
+
+@dataclass(frozen=True)
+class BoundingBox:
+    """Geographic bounding box expressed as WGS84 coordinates."""
+
+    name: str
+    north: float
+    south: float
+    east: float
+    west: float
+    description: str | None = None
+
+    def __post_init__(self) -> None:
+        if self.north <= self.south:
+            msg = f"north ({self.north}) must be greater than south ({self.south})"
+            raise ValueError(msg)
+        if self.east <= self.west:
+            msg = f"east ({self.east}) must be greater than west ({self.west})"
+            raise ValueError(msg)
+
+    def contains(self, latitude: float, longitude: float) -> bool:
+        """Return True when the given coordinate lies inside the bounding box."""
+
+        return (
+            self.south <= latitude <= self.north and self.west <= longitude <= self.east
+        )
+
+    def to_overpass_arg(self) -> str:
+        """Return the bbox string used for Overpass API queries."""
+
+        return f"{self.south},{self.west},{self.north},{self.east}"
+
+
+# Primary metropolitan areas we plan to support.
+DEFAULT_REGIONS: Tuple[BoundingBox, ...] = (
+    BoundingBox(
+        name="berlin_metropolitan",
+        north=52.6755,
+        south=52.3381,
+        east=13.7611,
+        west=13.0884,
+        description="Berlin and surrounding rapid transit network",
+    ),
+    BoundingBox(
+        name="hamburg_metropolitan",
+        north=53.7447,
+        south=53.3950,
+        east=10.3253,
+        west=9.7270,
+        description="Hamburg S-Bahn and harbor region",
+    ),
+    BoundingBox(
+        name="munich_metropolitan",
+        north=48.2485,
+        south=47.9960,
+        east=11.7229,
+        west=11.3600,
+        description="Munich S-Bahn core and airport corridor",
+    ),
+)
+
+
+# Tags that identify passenger stations and stops.
+STATION_TAG_FILTERS: Mapping[str, Tuple[str, ...]] = {
+    "railway": ("station", "halt", "stop"),
+    "public_transport": ("station", "stop_position", "platform"),
+    "train": ("yes", "regional", "suburban"),
+}
+
+
+def compile_overpass_filters(filters: Mapping[str, Iterable[str]]) -> str:
+    """Build an Overpass boolean expression that matches the provided filters."""
+
+    parts: list[str] = []
+    for key, values in filters.items():
+        options = "|".join(sorted(set(values)))
+        parts.append(f'  ["{key}"~"^({options})$"]')
+    return "\n".join(parts)
+
+
+__all__ = [
+    "BoundingBox",
+    "DEFAULT_REGIONS",
+    "STATION_TAG_FILTERS",
+    "compile_overpass_filters",
+]