Sprint 7: Gassi-Treffen — Meetup-Feature komplett

- Backend: walks.py mit allen Endpoints (CRUD, join/leave, Haversine-Filter)
- DB: walks, walk_participants, walk_participant_dogs Tabellen (bereits in database.py)
- Frontend: walks.js — Liste/Karte-Toggle, Heute/Demnächst-Gruppierung, Detail-Modal
  mit Teilnehmerliste, Beitreten/Verlassen, Erstellen/Bearbeiten-Formulare
- CSS: Walks-Komponenten (Card, Date-Badge, Spots-Anzeige, Map-View)
- api.js: walks-Abschnitt (list, get, create, update, cancel, join, leave)
- SW-Cache: by-v20 → by-v21

backend/static/js/api.js

@@ -190,6 +190,23 @@ const API = (() => {
     delete(id)       { return del(`/routes/${id}`); },
   };
 
+  // ----------------------------------------------------------
+  // GASSI-TREFFEN
+  // ----------------------------------------------------------
+  const walks = {
+    list(lat = null, lon = null, radius = 20000) {
+      const params = new URLSearchParams({ radius });
+      if (lat !== null) { params.set('lat', lat); params.set('lon', lon); }
+      return get(`/walks?${params}`);
+    },
+    get(id)           { return get(`/walks/${id}`); },
+    create(data)      { return post('/walks', data); },
+    update(id, data)  { return patch(`/walks/${id}`, data); },
+    cancel(id)        { return del(`/walks/${id}`); },
+    join(id, dogIds)  { return post(`/walks/${id}/join`, { dog_ids: dogIds }); },
+    leave(id)         { return del(`/walks/${id}/join`); },
+  };
+
   // ----------------------------------------------------------
   // WETTER
   // ----------------------------------------------------------
@@ -267,7 +284,7 @@ const API = (() => {
   return {
     get, post, put, patch, del, upload,
     auth, dogs, diary, health, tieraerzte, poison,
-    places, routes, weather, push,
+    places, routes, walks, weather, push,
     subscribeToPush, getLocation,
     APIError,
   };