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/app/service.go

@@ -244,8 +244,11 @@ func validatePoint(point store.Point) error {
 		return fmt.Errorf("%w: coordinates must have lon/lat", ErrBadRequest)
 	}
 	lon, lat := point.Coordinates[0], point.Coordinates[1]
-	if lon < -180 || lon > 180 || lat < -90 || lat > 90 {
-		return fmt.Errorf("%w: invalid lon/lat bounds", ErrBadRequest)
+	if lon < -180 || lon > 180 {
+		return fmt.Errorf("%w: longitude must be -180 to 180, got %.2f", ErrBadRequest, lon)
+	}
+	if lat < -90 || lat > 90 {
+		return fmt.Errorf("%w: latitude must be -90 to 90, got %.2f", ErrBadRequest, lat)
 	}
 	return nil
 }
@@ -272,6 +275,33 @@ func (s *Service) ListCollections(ownerKey string) []store.Collection {
 	return s.store.ListCollectionsByOwner(ownerKey)
 }
 
+func (s *Service) UpdateCollection(ownerKey, collectionID, name string) (store.Collection, error) {
+	collection, err := s.store.GetCollection(collectionID)
+	if err != nil {
+		return store.Collection{}, ErrCollectionMiss
+	}
+	if collection.OwnerKey != ownerKey {
+		return store.Collection{}, ErrForbidden
+	}
+	if name == "" {
+		return store.Collection{}, fmt.Errorf("%w: collection name required", ErrBadRequest)
+	}
+	collection.Name = name
+	s.store.SaveCollection(collection)
+	return collection, nil
+}
+
+func (s *Service) DeleteCollection(ownerKey, collectionID string) error {
+	collection, err := s.store.GetCollection(collectionID)
+	if err != nil {
+		return ErrCollectionMiss
+	}
+	if collection.OwnerKey != ownerKey {
+		return ErrForbidden
+	}
+	return s.store.DeleteCollection(collectionID)
+}
+
 func (s *Service) CreateFeature(ownerKey, collectionID string, geometry store.Point, properties map[string]interface{}) (store.Feature, error) {
 	collection, err := s.store.GetCollection(collectionID)
 	if err != nil {