feat(transit): add Szczecin buses and trams (ZDiTM, CC0)

Keyless GTFS-Realtime feed published by ZDiTM Szczecin under CC0 1.0.
Speeds are m/s (checked against vehicle movement), the file refreshes about
every 20 s, and the feed carries no route ids, so vehicles take the default
bus mode.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

README.md

@@ -444,7 +444,7 @@ Twenty-one layers and map sources. **Nineteen have a keyless path.** Some offer
 | 📷 **Mapped ALPR Cameras**  | License-plate-reader camera locations tagged by OpenStreetMap contributors, loaded one city-sized view at a time, with **SHOW NEAREST**. Locations and tags only: no plate data, no video                                                                                                                                                                                           | OpenStreetMap (incl. DeFlock mapping)   | 🟢                                                                                                  |
 | 📷 **Street Level**         | Street-level photos behind one panel, one chip per provider: coverage on the streets, image cones, an embedded viewer with full-screen **EXPAND**. Mapillary, Google Street View, KartaView and Panoramax | Mapillary · Google · KartaView · Panoramax | 🟢 KartaView, Panoramax · 🟡 Mapillary token · 🔴 Google Maps key |
 | 📻 **Radio**                | Geolocated world radio with an **analog tuner** — drag the needle across up to 750 stations and the globe flies to each broadcaster                                                                                                                                                                                                                                                 | Radio Browser / broadcasters            | 🟢                                                                                                  |
-| 🚌 **Transit**              | Live buses, trams, metros, trains and ferries with delayed playback between reports, selected-vehicle trails, and mode-coloured DETECT labels — Boston, Austin, Minneapolis, Helsinki, the Netherlands, Norway, South East Queensland, Rio de Janeiro (buses and BRT), and nine in Ontario: Toronto (surface vehicles; the subway publishes no positions), Mississauga, Hamilton, Durham Region, York Region, Guelph, Burlington, Barrie and Kingston                                                                                                                                               | Operator GTFS-Realtime feeds            | 🟢                                                                                                  |
+| 🚌 **Transit**              | Live buses, trams, metros, trains and ferries with delayed playback between reports, selected-vehicle trails, and mode-coloured DETECT labels — Boston, Austin, Minneapolis, Helsinki, the Netherlands, Norway, South East Queensland, Rio de Janeiro (buses and BRT), Szczecin, and nine in Ontario: Toronto (surface vehicles; the subway publishes no positions), Mississauga, Hamilton, Durham Region, York Region, Guelph, Burlington, Barrie and Kingston                                                                                                                                               | Operator GTFS-Realtime feeds            | 🟢                                                                                                  |
 | 🚲 **Bikeshare**            | Live station availability                                                                                                                                                                                                                                                                                                                                                           | GBFS                                    | 🟢                                                                                                  |
 | 🧭 **Directions**           | Click A and B on the globe for a street-following drive, walk or cycle route draped on the terrain with turn-by-turn steps — then FLY the camera along it. No key, no geocoder, no mic                                                                                                                                                                                              | OSRM on FOSSGIS servers (OpenStreetMap) | 🟢                                                                                                  |
 | ⌖ **OSM Places**           | Voice place search ("hospitals in Kathmandu") from OpenStreetMap, drawn as numbered points that follow-up questions can filter. Needs your own Overpass server (`OVERPASS_UPSTREAMS`); off otherwise                                                                                                                                                                                                                                                                                                                               |