fix OpenBSD installer: disambiguate fish, add Rust for shell-gpt

- Use fish%main branch selector to install fish 4.x (avoids 3.x/4.x ambiguity)
- Add rust package so jiter/pydantic-core can compile from source
- Redirect pipx/cargo/pip temp dirs to /tmp on OpenBSD (root partition too small)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

run_onchange_after_install_main_deps.sh.tmpl

@@ -392,7 +392,7 @@ $SUDO pkg install --yes $ACT_PACKAGES neovim fish atuin lazygit fd-find pam_ssh_
 
 {{ else if eq .chezmoi.os "openbsd" -}}
 
-$SUDO pkg_add neovim fish fd ripgrep unzip-- htop fzf bat gawk jq nnn-- mc ngrep mtr-- gcc%11 2>&1|pad
+$SUDO pkg_add neovim fish%main rust fd ripgrep unzip-- htop fzf bat gawk jq nnn-- mc ngrep mtr-- gcc%11 2>&1|pad
 
 {{ else if eq .chezmoi.os "darwin" -}}
     brew install -q fish neovim $ACT_PACKAGES atuin jump fd sk dust lazygit 2>&1|pad
@@ -459,7 +459,11 @@ fi
 {{ end -}}
 
 new_line "Installing shell-gpt"
+{{ if eq .chezmoi.os "openbsd" -}}
+$SUDO sh -c 'TMPDIR=/tmp CARGO_HOME=/tmp/cargo PIP_CACHE_DIR=/tmp/pip-cache PIPX_HOME=/usr/local/lib/pipx PIPX_BIN_DIR=/usr/local/bin pipx install shell-gpt' 2>&1|pad
+{{ else -}}
 pipx install shell-gpt  2>&1|pad
+{{ end -}}
 
 new_line "Install fisher plugin manager for fish"
 ## Install fisher plugin manager for fish, so that we may update in after plugin list sync by chezmoi