Add modular dev environment installer, dotfiles, and desnap script

Adds a TUI-driven, rollback-capable installer (install/install.sh +
install/modules/*.sh) covering JS/Python/systems toolchains, dev tooling,
browsers, chat apps, GNOME extras, and misc setup (wakatime key, ssh/gpg
perms, apt mirror benchmarking), all sourced from each vendor's official
install method. bootstrap.sh stows the zsh/git/tmux/vscode dotfiles and
runs the installer; desnap.sh purges snapd and replaces default snaps with
apt/Flatpak equivalents.

install/modules/ghcli.sh

@@ -0,0 +1,7 @@
+install_ghcli() {
+  if has_cmd gh; then ok "gh already installed"; return; fi
+  apt_add_repo github-cli /etc/apt/keyrings/githubcli-archive-keyring.gpg \
+    https://cli.github.com/packages/githubcli-archive-keyring.gpg \
+    "deb [arch=$(deb_arch) signed-by=/etc/apt/keyrings/githubcli-archive-keyring.gpg] https://cli.github.com/packages stable main"
+  apt_install gh
+}