feat(blankpad): desk.sh profile switcher, hotplug autoswitch daemon, keybinds doc generator + bats suite

- desk.sh: list/current/switch/cycle/match/capture over cfg/desk-*.kdl
  profiles; apply = relink display.kdl, niri validate (rollback on fail),
  load-config-file, noctalia notification; match scores // requires: lines
  (EDID long names) against live niri msg outputs
- desk-autoswitch.sh: watch niri msg --json event-stream for
  OutputsChanged, debounced desk.sh match --apply, reconnect loop
- blankpad-desk-autoswitch.service: ConditionHost=blankpad user unit
- gen-keybinds.sh: keybinds.kdl -> markdown cheat sheet (sections from
  // --- headers, hotkey-overlay-title preferred over action)
- tests/: 27 bats cases, all green (desk 16, gen-keybinds 6,
  niri-config 5 incl. real niri validate on the assembled tree with
  each desk profile active)

scripts/desk-autoswitch.sh

@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+# scripts/desk-autoswitch.sh — hotplug daemon: apply the matching desk profile
+# whenever niri reports an OutputsChanged event.
+#
+# Usage: desk-autoswitch.sh watch
+#
+# Environment overrides:
+#   DESK_AUTO_HOSTNAME  only run on this hostname (default: blankpad)
+#   DESK_SCRIPT         path to desk.sh (default ~/.local/bin/desk.sh)
+#   DESK_NIRI           niri binary (default niri)
+#   DESK_DEBOUNCE_S     debounce window in seconds (default 1.5)
+
+set -euo pipefail
+
+HOST="${DESK_AUTO_HOSTNAME:-blankpad}"
+DESK="${DESK_SCRIPT:-$HOME/.local/bin/desk.sh}"
+NIRI="${DESK_NIRI:-niri}"
+DEBOUNCE="${DESK_DEBOUNCE_S:-1.5}"
+
+usage() {
+  sed -n '2,12p' "$0" | sed 's/^# \{0,1\}//'
+}
+
+watch_mode() {
+  [ "$(hostname)" = "$HOST" ] || { echo "desk-autoswitch: not on $HOST, exiting"; exit 0; }
+  echo "desk-autoswitch: initial match"
+  "$DESK" match --apply || true
+
+  local last=0 now
+  # One JSON event per line; reconnect forever (niri restart drops the stream).
+  while "$NIRI" msg --json event-stream 2>/dev/null | while IFS= read -r line; do
+    case "$line" in
+      *OutputsChanged*)
+        now="$(date +%s.%N)"
+        # swallow bursts inside the debounce window
+        if awk -v l="$last" -v n="$now" -v d="$DEBOUNCE" 'BEGIN { exit !(n - l >= d) }'; then
+          last="$now"
+          echo "desk-autoswitch: OutputsChanged"
+          "$DESK" match --apply || true
+        fi
+        ;;
+    esac
+  done; do :; done
+}
+
+case "${1:-}" in
+  watch) watch_mode ;;
+  -h|--help) usage ;;
+  *) usage >&2; exit 1 ;;
+esac