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/store/interface.go

@@ -16,6 +16,7 @@ type Store interface {
 	SaveCollection(c Collection)
 	ListCollectionsByOwner(owner string) []Collection
 	GetCollection(id string) (Collection, error)
+	DeleteCollection(id string) error
 	SaveFeature(f Feature)
 	ListFeaturesByCollection(collectionID string) []Feature
 	GetFeature(featureID string) (Feature, error)

internal/store/memory.go

@@ -157,6 +157,21 @@ func (s *MemoryStore) GetCollection(id string) (Collection, error) {
 	return c, nil
 }
 
+func (s *MemoryStore) DeleteCollection(id string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if _, ok := s.collections[id]; !ok {
+		return ErrNotFound
+	}
+	for fid, f := range s.features {
+		if f.CollectionID == id {
+			delete(s.features, fid)
+		}
+	}
+	delete(s.collections, id)
+	return nil
+}
+
 func (s *MemoryStore) SaveFeature(f Feature) {
 	s.mu.Lock()
 	defer s.mu.Unlock()

internal/store/postgres.go

@@ -204,6 +204,18 @@ func (s *PostgresStore) GetCollection(id string) (Collection, error) {
 	return c, nil
 }
 
+func (s *PostgresStore) DeleteCollection(id string) error {
+	res, err := s.db.Exec(`DELETE FROM collections WHERE id = $1`, id)
+	if err != nil {
+		return err
+	}
+	n, _ := res.RowsAffected()
+	if n == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
 func (s *PostgresStore) SaveFeature(f Feature) {
 	geom, _ := json.Marshal(f.Geometry)
 	props, _ := json.Marshal(f.Properties)