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/zig.sh

@@ -0,0 +1,65 @@
+install_zig() {
+  local index latest
+  index=$(curl -fsSL https://ziglang.org/download/index.json)
+  latest=$(jq -r 'keys[]' <<< "$index" | grep -v '^master$' | sort -V | tail -n1)
+
+  if has_cmd zig && zig version 2>/dev/null | grep -qx "$latest"; then
+    ok "zig already at $latest"
+  else
+    local url tarball extract_dir
+    url=$(jq -r --arg v "$latest" '.[$v]["x86_64-linux"].tarball' <<< "$index")
+    tarball=$(mktemp --suffix=.tar.xz)
+    curl -fsSL "$url" -o "$tarball"
+
+    extract_dir=$(mktemp -d)
+    tar -xJf "$tarball" -C "$extract_dir" --strip-components=1
+    rm -f "$tarball"
+
+    sudo rm -rf /opt/zig
+    track_new_sudo_dir /opt/zig
+    sudo mv "$extract_dir" /opt/zig
+    sudo ln -sf /opt/zig/zig /usr/local/bin/zig
+    rollback_push "sudo rm -f /usr/local/bin/zig"
+  fi
+
+  _zig_install_zls
+}
+
+# zls (the Zig language server) is versioned against a specific zig build;
+# zigtools' own select-version API returns the right zls release for
+# whatever zig version is currently installed.
+_zig_install_zls() {
+  if ! has_cmd zig; then return 0; fi
+
+  local zig_version resp url
+  zig_version=$(zig version)
+  resp=$(curl -fsSL "https://releases.zigtools.org/v1/zls/select-version?zig_version=${zig_version}&compatibility=only-runtime")
+  url=$(jq -r '.["x86_64-linux"].tarball // empty' <<< "$resp" 2>/dev/null)
+
+  if [[ -z "$url" ]]; then
+    warn "no matching zls build for zig $zig_version, skipping"
+    return 0
+  fi
+
+  if [[ -x /opt/zls/zls ]]; then
+    local current
+    current=$(/opt/zls/zls --version 2>/dev/null || echo "")
+    if [[ "$current" == *"$zig_version"* ]]; then
+      ok "zls already matches zig $zig_version"
+      return 0
+    fi
+  fi
+
+  local tarball extract_dir
+  tarball=$(mktemp --suffix=.tar.xz)
+  curl -fsSL "$url" -o "$tarball"
+  extract_dir=$(mktemp -d)
+  tar -xJf "$tarball" -C "$extract_dir"
+  rm -f "$tarball"
+
+  sudo rm -rf /opt/zls
+  track_new_sudo_dir /opt/zls
+  sudo mv "$extract_dir" /opt/zls
+  sudo ln -sf /opt/zls/zls /usr/local/bin/zls
+  rollback_push "sudo rm -f /usr/local/bin/zls"
+}