AGENTS.md had grown to 355 lines. Move the detailed architecture, model
and node sections into docs/agents/ and keep the root file to the rules
that should steer every change. All existing rules are preserved.
Add CLAUDE.md as a regular file containing an @AGENTS.md import so Claude
Code reads the same instructions. The previous attempt used a symlink,
which broke updates and was reverted in 7cf4e78.
