Add OSM Track Harvesting Policy and demo database initialization script

- Updated documentation to include OSM Track Harvesting Policy with details on railway types, service filters, usage filters, and geometry guardrails.
- Introduced a new script `init_demo_db.py` to automate the database setup process, including environment checks, running migrations, and loading OSM fixtures for demo data.

backend/tests/test_tracks_load.py

@@ -166,3 +166,35 @@ def test_load_tracks_skips_existing_pairs(monkeypatch: pytest.MonkeyPatch) -> No
     assert created == 0
     assert session_instance.rolled_back is True
     assert not track_repo_instance.created
+
+
+def test_load_tracks_skips_when_station_too_far(monkeypatch: pytest.MonkeyPatch) -> None:
+    session_instance = DummySession()
+    station_repo_instance = DummyStationRepository(
+        session_instance,
+        stations=[
+            DummyStation(id="remote-station", location=_point(53.5, 14.5)),
+        ],
+    )
+    track_repo_instance = DummyTrackRepository(session_instance)
+
+    monkeypatch.setattr(tracks_load, "SessionLocal", lambda: session_instance)
+    monkeypatch.setattr(tracks_load, "StationRepository",
+                        lambda session: station_repo_instance)
+    monkeypatch.setattr(tracks_load, "TrackRepository",
+                        lambda session: track_repo_instance)
+
+    parsed = tracks_load._parse_track_entries(
+        [
+            {
+                "name": "Isolated Segment",
+                "coordinates": [[52.5, 13.4], [52.51, 13.41]],
+            }
+        ]
+    )
+
+    created = tracks_load.load_tracks(parsed, commit=True)
+
+    assert created == 0
+    assert session_instance.committed is True
+    assert not track_repo_instance.created