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.

dot_config/foot/patch.py

@@ -0,0 +1,25 @@
+from pathlib import Path
+p = Path("/home/rain/.config/foot/foot.ini")
+text = p.read_text()
+old_lines = [
+    "# foot does not expand env variables in the `shell=` value, so we have to",
+    "# go through `sh -c` to make the parent's $SHELL take effect. When foot",
+    "# is launched from a fish session, $SHELL is /bin/fish, and foot runs fish.",
+    "# When launched from bash, $SHELL is /bin/bash, and foot runs bash. The",
+    "# default fallback is /bin/bash if $SHELL is unset for any reason.",
+    'shell=sh,-c,"exec ${SHELL:-/bin/bash} -i"',
+]
+new_lines = [
+    "# kaiser runs zsh as the login shell. Hardcode /usr/bin/zsh here.",
+    "# foot does NOT expand $SHELL in shell= (it passes the literal string",
+    "# to its child process), so the sh,-c trick makes foot try to exec a",
+    '# binary literally named "${SHELL:-/bin/bash}" and die with',
+    '# "No such file or directory". Point shell= at the binary directly.',
+    "shell=/usr/bin/zsh",
+]
+old = "\n".join(old_lines)
+new = "\n".join(new_lines)
+assert old in text, "old block not found in foot.ini"
+text = text.replace(old, new, 1)
+p.write_text(text)
+print("OK, new size:", len(text))