Renomme excalidraw-go en excalicloud

Module Go github.com/vblogio/excalicloud (imports internes mis à jour),
image Docker excalicloud:local, paquet npm excalicloud-frontend,
champ source des exports .excalidraw, README et THIRD_PARTY_NOTICES.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019MgtkAhkuqFbMAuTgTDeFh

frontend/src/Explorer.tsx

@@ -59,7 +59,7 @@ import { Thumb } from "./Thumb";
 export const EMPTY_SCENE = JSON.stringify({
   type: "excalidraw",
   version: 2,
-  source: "excalidraw-go",
+  source: "excalicloud",
   elements: [],
   appState: {},
   files: {},