feat(install): optional add-ons via --with and interactive prompt

Wire install_<name>.sh into the main installer through a shared catalog
so fnm/pyenv/nvm (and future tools) share one CLI and prompt path.

README.md

@@ -10,10 +10,21 @@ fzf-tab, k), plus eza, zoxide, fzf, and Nerd Fonts.
 curl -fsSL https://git.miomio.moe/mio/easyzsh/raw/branch/master/install.sh | bash
 ```
 
-Options: `--cp-hist` / `-c` imports bash history; `--non-interactive` / `-n`
-skips the default-shell change.
+Options:
 
-From a git checkout:
+- `--cp-hist` / `-c` — import bash history
+- `--non-interactive` / `-n` — skip default-shell change and optional prompts
+- `--with <names>` — install optional add-ons (comma-separated, repeatable).
+  Each name runs `install_<name>.sh` (currently: `fnm`, `pyenv`, `nvm`).
+  Interactive installs (without `-n` and without `--with`) prompt for the same list.
+
+```bash
+./install.sh --with fnm
+./install.sh --with fnm,pyenv -n
+curl -fsSL …/install.sh | bash -s -- --with fnm
+```
+
+From a git checkout (shell stubs only):
 
 ```bash
 ./deploy.sh