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/firefox.sh

@@ -0,0 +1,20 @@
+install_firefox() {
+  if [[ -f /etc/apt/preferences.d/mozilla ]]; then
+    ok "firefox (deb) already installed"
+    return
+  fi
+
+  log "removing snap firefox / transitional apt stub in favor of Mozilla's official apt repo"
+  sudo apt-get remove -y firefox 2>/dev/null || true
+  sudo snap remove firefox 2>/dev/null || true
+
+  apt_add_repo mozilla /etc/apt/keyrings/packages.mozilla.org.asc \
+    https://packages.mozilla.org/apt/repo-signing-key.gpg \
+    "deb [signed-by=/etc/apt/keyrings/packages.mozilla.org.asc] https://packages.mozilla.org/apt mozilla main"
+
+  printf 'Package: *\nPin: origin packages.mozilla.org\nPin-Priority: 1000\n' \
+    | sudo tee /etc/apt/preferences.d/mozilla >/dev/null
+  rollback_push "sudo rm -f /etc/apt/preferences.d/mozilla"
+
+  apt_install firefox
+}