Remove the Departures screen

Not needed any more -- the Journey screen already covers the same
regional-transit need via EFA backends, and Departures depended on
the free db-vendo-client API that DB has been actively blocking third
parties from anyway.

Removed screens/departures.py, its settings template, its route, its
registration in screens/__init__.py, and its nav link. Reworded the
docstring/hint references in journey.py and settings_journey.html
that pointed at the now-gone screen. Existing config.json entries
referencing "departures" (rotation list, pinned screen) are harmless
leftovers -- both scheduler lookups already filter to screens that
still exist, so nothing needs a migration step.

Verified: app boots clean, /settings/departures 404s, every other
settings page still loads fine, no leftover references outside of
journey.py's own unrelated "departure time" wording.

web/app.py

@@ -128,40 +128,6 @@ def create_app(config, screens: dict, scheduler) -> Flask:
 
         return render_template("settings_weather.html", settings=config.get_screen_settings("weather"), error=error)
 
-    @app.route("/settings/departures", methods=["GET", "POST"])
-    def settings_departures():
-        error = None
-        if request.method == "POST":
-            station_query = request.form.get("station", "").strip()
-            results = int(request.form.get("results", 5) or 5)
-            if results not in (3, 5, 8):
-                results = 5
-            update_minutes = max(1, int(request.form.get("update_minutes", 2) or 2))
-
-            if station_query:
-                try:
-                    found = screens["departures"].find_station(station_query)
-                except requests.exceptions.RequestException:
-                    found = None
-                if found is None:
-                    error = f'Could not find a station matching "{station_query}" -- try a different spelling, or the service might be temporarily down.'
-                else:
-                    config.update_screen_settings("departures", {
-                        "station": station_query,
-                        "station_id": found["id"],
-                        "station_label": found["name"],
-                        "results": results,
-                        "update_minutes": update_minutes,
-                    })
-                    scheduler.invalidate_screen("departures")
-                    return redirect(url_for("settings_departures", found=found["name"]))
-            else:
-                config.update_screen_settings("departures", {"results": results, "update_minutes": update_minutes})
-                scheduler.invalidate_screen("departures")
-                return redirect(url_for("settings_departures", saved=1))
-
-        return render_template("settings_departures.html", settings=config.get_screen_settings("departures"), error=error)
-
     @app.route("/settings/journey", methods=["GET", "POST"])
     def settings_journey():
         error = None