sway: factor env restoration into restore-wayland-env.sh, fix caffeine notify

caffeine.sh click was working (icon toggled, swayidle restarted) but
the 'Caffeine ON/OFF' notification never appeared. Same root cause as
the prior swayidle bug: waybar's on-click context strips WAYLAND_DISPLAY
from the spawned script's env. notify-send writes to D-Bus (exit 0) but
mako can't display because it has no Wayland socket to render on. Click
appears to do nothing visually.

Fix: extract the /proc/*/environ probe into a shared helper
(restore-wayland-env.sh) and source it from both caffeine.sh AND
start-swayidle.sh. Now any future on-click script in this repo can
`. restore-wayland-env.sh` to inherit the right env.

Verified on tadbit:
- click 1 (caffeine ON): swayidle killed, flag set, 'Caffeine ON'
  notification appeared in mako
- click 2 (caffeine OFF): swayidle restarted, flag cleared, 'Caffeine
  OFF' notification appeared in mako

Both are visible in makoctl history now.

dot_config/sway/restore-wayland-env.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+# restore-wayland-env.sh — probe /proc for a running Wayland client and
+# inherit its WAYLAND_DISPLAY / DISPLAY / DBUS_SESSION_BUS_ADDRESS /
+# XDG_RUNTIME_DIR. Used by caffeine.sh and start-swayidle.sh so on-click
+# scripts run from waybar's context (which doesn't inherit the Sway env)
+# can still talk to the compositor.
+#
+# Why probe /proc? waybar's on-click handler forks the script in waybar's
+# own process context. That context has WAYLAND_DISPLAY set (waybar is a
+# Wayland client), but other Sway context (XDG_CURRENT_DESKTOP, sway IPC
+# socket, etc.) isn't passed to children. We need WAYLAND_DISPLAY for
+# swaymsg/grim/wl-copy/notify-send, so the env-restoration here covers the
+# "Wayland client tools" subset. Swaymsg-specific env (I3SOCK / SWAYSOCK)
+# isn't included because swaymsg falls back to discovery via the
+# /run/user/UID/sway-ipc.*.sock path.
+#
+# Idempotent: if WAYLAND_DISPLAY and DISPLAY are already set, does nothing.
+# Source-able: `source "$HOME/.config/sway/restore-wayland-env.sh"`.
+
+if [[ -n "$WAYLAND_DISPLAY" || -n "$DISPLAY" ]]; then
+    return 0 2>/dev/null || exit 0
+fi
+
+# Find a running Wayland client. mako, swaybar, foot, wofi — anything
+# bound to wayland-N. We grab the first one with WAYLAND_DISPLAY set.
+for pid in /proc/[0-9]*; do
+    [[ -r "$pid/environ" ]] || continue
+    candidate=$(tr '\0' '\n' < "$pid/environ" 2>/dev/null | grep -E '^(WAYLAND_DISPLAY|DISPLAY|DBUS_SESSION_BUS_ADDRESS|XDG_RUNTIME_DIR)=' || true)
+    if [[ -n "$candidate" ]]; then
+        # shellcheck disable=SC2086
+        export $candidate
+        return 0 2>/dev/null || exit 0
+    fi
+done