install.sh: install Claude Code if not already present

Adds a step after personal-dotfile deploy that runs Anthropic's
official one-liner installer (curl -fsSL https://claude.ai/install.sh | bash)
when no 'claude' binary is found. No-ops if claude is already on the
machine. Opt out with DRUNKENDOTFILES_SKIP_CLAUDE=1. Install failures
are non-fatal — the rest of the flow still completes.

README: document the new step + the opt-out env var + curl in the
required tools list.

README.md

@@ -33,8 +33,11 @@ The installer:
 2. Runs YADR's native `rake install` for vim/prezto/plugins
 3. Deploys the personal dotfiles on top of `$HOME`, moving any collisions to
    `~/.drunkendotfiles.bak.<timestamp>/`
+4. Installs [Claude Code](https://claude.ai/code) (Anthropic's CLI) if it
+   isn't already on the machine — set `DRUNKENDOTFILES_SKIP_CLAUDE=1` to
+   skip this step
 
-Requires `git` and `rake` (ruby).
+Requires `git`, `rake` (ruby), and `curl`.
 
 ## Upgrading