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/rust.sh

@@ -0,0 +1,7 @@
+install_rust() {
+  if has_cmd rustc; then ok "rust already installed"; return; fi
+  track_new_dir "$HOME/.cargo"
+  track_new_dir "$HOME/.rustup"
+  curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --no-modify-path
+  profile_add '. "$HOME/.cargo/env"'
+}