[docs] Add CLI-Direct approach guide for terminal-based AI tools

Documents how CLI AI tools (Claude Code, Codex, Gemini CLI) can interact
with Open Brain directly via shell commands, bypassing MCP. Includes the
complete `ob` CLI bash script, architecture comparisons, embedding pipeline
solutions, activation controls, and per-tool configuration instructions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: az9713