docs: split development documentation into dedicated page

docs: split development documentation into dedicated page

Move the technical architecture, install.sh, project structure, database
layout, Hermes Agent integration, and development workflow sections from
the main doc/index.org into a new doc/development/index.org file.

The main index now keeps a shorter "Source code" section with the
license, author, and source-code links, and links to the new dedicated
Development page. This mirrors the branching documentation structure
used in the sixth-3d project.