docs(wiki): complete imPress v2.1 wiki 24 pages, written from the repository's documentation and checked against the code: concepts and glossary, system architecture, protocols and mesh, installation, hardware guide, firmware build and flash, configuration reference, administrator and teacher guides, CSV imports, device management, firmware management and OTA, security, troubleshooting, recovery procedures, database and migrations, API reference, development guide, testing and CI, FAQ, release notes, sidebar and footer. Every internal link and anchor resolves. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>