feat: Codex support in wanderbooks new; the site leads with 'free, turn Claude or Codex into a full bookkeeping system'

wanderbooks new --codex registers the books' MCP server with Codex (as
wanderbooks-<dir>) and starts Codex; the scaffolded justfile gains codex
and codex-setup. The site drops 'hire', says free up front, shows
Claude Code or Codex + wanderbooks = a complete bookkeeping system, and
explains MCP and cost in the FAQ.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MtYEaR6M6Ybdhm6X98BWNu

README.md

@@ -67,7 +67,8 @@ books dir with the MCP server registered for it, and starts the agent):
 curl -fsSL https://wanderbooks.ai/install.sh | sh -s -- ~/Books/Acme
 ```
 
-Already installed: `wanderbooks new ~/Books/Acme`. In a books dir, `just`
+Already installed: `wanderbooks new ~/Books/Acme` (add `--codex` to keep the
+books with Codex instead of Claude Code). In a books dir, `just`
 lists the shortcuts (`just gui`, `just agent`, `just backup`).
 
 ## Layout