Add sway/wofi/foot Wayland desktop stack with per-host toggle

New opt-in feature for x86_64 desktops: sway + wofi + foot + swaybg +
swaylock + swayidle + grim + slurp + waybar + wl-clipboard. mako on
arch, dunst on debian (mako isn't packaged for debian).

Files:
- .chezmoi.yaml.tmpl: added data.sway flag (true on miche/byte/kaiser,
  false on Pis). Override per host with ~/.config/chezmoi/features/sway
  or ~/.config/chezmoi/features/no-sway marker files.
- run_once_40-install-sway.sh.tmpl: installs packages if .sway=true,
  exits 0 otherwise. Sets up the marker file.
- dot_config/{sway,foot,wofi,waybar,mako}/: existing configs from miche.

Per-host toggle workflow:
  # On any box, enable sway:
  touch ~/.config/chezmoi/features/sway
  chezmoi apply

  # On a sway-enabled box, disable it:
  touch ~/.config/chezmoi/features/no-sway
  rm ~/.config/chezmoi/features/sway
  chezmoi apply

Currently sway packages are already installed on miche (existed before
this commit). Byte will get them via the new run_once_40 script.
Pis (rye, crouton) are unaffected — install script early-returns.

run_once_40-install-sway.sh.tmpl

@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+# =============================================================================
+#  run_once_40-install-sway.sh.tmpl
+#  Install the sway + wofi + foot + supporting tooling desktop stack.
+#
+#  Gated on .sway (set in .chezmoi.yaml.tmpl). When false (Pis, headless
+#  boxes, etc.), this script exits 0 without doing anything.
+#
+#  To opt a new box in: `touch ~/.config/chezmoi/features/sway` then
+#  `chezmoi apply`. To opt out: `touch ~/.config/chezmoi/features/no-sway`.
+#
+#  Idempotent: skips if sway is already installed.
+# =============================================================================
+set -euo pipefail
+
+log() { printf '\033[1;34m[sway]\033[0m %s\n' "$*"; }
+
+# --- 0. Gate on the .sway flag ---
+{{ if not .sway -}}
+log "sway not enabled for this host (.sway=false). Skipping."
+log "To enable: touch ~/.config/chezmoi/features/sway && chezmoi apply"
+exit 0
+{{ end -}}
+
+# --- 1. Install packages ---
+SWAY_PKGS=(sway wofi foot swaybg swaylock swayidle grim slurp waybar wl-clipboard)
+
+{{ if eq .os_family "arch" -}}
+# mako is in arch [extra]
+SWAY_PKGS+=(mako)
+{{ else if eq .os_family "debian" -}}
+# mako isn't packaged on debian. Use dunst (lightweight notification daemon,
+# widely compatible with sway/waybar setups).
+SWAY_PKGS+=(dunst)
+{{ else -}}
+log "WARNING: sway packages not configured for os_family={{ .os_family }}"
+{{ end -}}
+
+log "installing sway stack: ${SWAY_PKGS[*]}"
+
+{{ if eq .os_family "arch" -}}
+sudo pacman -S --needed --noconfirm "${SWAY_PKGS[@]}"
+{{ else if eq .os_family "debian" -}}
+export DEBIAN_FRONTEND=noninteractive
+sudo apt-get install -y --no-install-recommends "${SWAY_PKGS[@]}"
+{{ end -}}
+
+log "sway stack installed"
+sway --version 2>&1 | head -1
+foot --version 2>&1 | head -1
+wofi --version 2>&1 | head -1
+
+# --- 2. Mark the box so subsequent chezmoi applies know sway is enabled ---
+mkdir -p ~/.config/chezmoi/features
+touch ~/.config/chezmoi/features/sway
+log "marked box: ~/.config/chezmoi/features/sway"
+
+log "sway stack install complete"