Docs still describe the 26.11.1 pre-release situation #275

Both 26.11.1 finals are on PyPI now, but the README and five docs pages still describe the pre-release situation: a transition note saying arcadedb may appear only as 26.11.1.devN, a --prerelease allow hint in the quickstart and the migration steps, a bulk-load note that starts from 26.11.1.devN, and the install-check output printing 26.11.1.dev2.

I will reword them for the finals. I ran the install-check script from the installation page against the published arcadedb==26.11.1 wheel and it prints 26.11.1 and Backend: native, so the sample output can change too.