Demo app, collections/features CRUD, QR codes, docs

Demo app (web/):
- Collections: select, rename, remove (x button per row), delete
- Features: add point (lon/lat validation), remove, list in selected collection
- QR codes for pk (private) and pb (public) keys
- Restore public key from private key
- 409 Conflict handled for already-registered login
- Title: Momswap Geo Backend Use-Cases Test

Backend:
- PATCH /v1/collections/{id} for rename
- DELETE /v1/collections/{id}
- Clearer lon/lat validation errors (-180..180, -90..90)

Client:
- updateCollection, deleteCollection, derivePublicKey

Docs:
- docs/frontend-development.md (demo app, local dev)
- README links to all docs

Made-with: Cursor

internal/http/handlers.go

@@ -35,6 +35,8 @@ func (a *API) Routes() http.Handler {
 
 	mux.HandleFunc("POST /v1/collections", a.createCollection)
 	mux.HandleFunc("GET /v1/collections", a.listCollections)
+	mux.HandleFunc("PATCH /v1/collections/{id}", a.updateCollection)
+	mux.HandleFunc("DELETE /v1/collections/{id}", a.deleteCollection)
 	mux.HandleFunc("POST /v1/collections/{id}/features", a.createFeature)
 	mux.HandleFunc("GET /v1/collections/{id}/features", a.listFeatures)
 	mux.HandleFunc("DELETE /v1/features/{id}", a.deleteFeature)
@@ -272,6 +274,42 @@ func (a *API) listCollections(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, map[string]interface{}{"collections": a.service.ListCollections(user)})
 }
 
+func (a *API) updateCollection(w http.ResponseWriter, r *http.Request) {
+	user, err := a.authUser(r)
+	if err != nil {
+		writeErr(w, err)
+		return
+	}
+	collectionID := r.PathValue("id")
+	var req struct {
+		Name string `json:"name"`
+	}
+	if err := readJSON(r, &req); err != nil {
+		writeErr(w, app.ErrBadRequest)
+		return
+	}
+	collection, err := a.service.UpdateCollection(user, collectionID, req.Name)
+	if err != nil {
+		writeErr(w, err)
+		return
+	}
+	writeJSON(w, http.StatusOK, collection)
+}
+
+func (a *API) deleteCollection(w http.ResponseWriter, r *http.Request) {
+	user, err := a.authUser(r)
+	if err != nil {
+		writeErr(w, err)
+		return
+	}
+	collectionID := r.PathValue("id")
+	if err := a.service.DeleteCollection(user, collectionID); err != nil {
+		writeErr(w, err)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
 func (a *API) createFeature(w http.ResponseWriter, r *http.Request) {
 	user, err := a.authUser(r)
 	if err != nil {