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

libs/geo-api-client/src/keys.ts

@@ -17,6 +17,12 @@ export async function generateKeyPair(): Promise<StoredKeys> {
   };
 }
 
+export async function getPublicKeyFromPrivate(privateKeyBase64: string): Promise<string> {
+  const privateKey = base64UrlToBytes(privateKeyBase64);
+  const publicKey = await getPublicKeyAsync(privateKey);
+  return bytesToBase64Url(publicKey);
+}
+
 export async function signMessage(privateKeyBase64: string, message: string): Promise<string> {
   const privateKey = base64UrlToBytes(privateKeyBase64);
   const signature = await signAsync(textToBytes(message), privateKey);