test(docking): prove the keyboard-restore path; the reload clobber is real

The last unproven half of bec826b, and it needed a keyboard that stays behind
when the dock leaves. The dev box's by-tech hangs off the BenQ's own hub, so
it always walked away with the cable — a Logitech K400 with its receiver in
the laptop is the real case, and Bernardo happened to plug one in.

Both halves measured on hardware (dev box, 2026-07-14):

  - PRIMARY: across a real unplug + the fixed transition, the K400 kept its
    remembered `us`. Panel back, layout intact.
  - CONTROL: a bare `hyprctl reload` with no restore took the same board from
    `us` to the session's `gb`.

The control matters more than the pass. That reload clobbers runtime
`device[<name>]:kb_layout` was an inference from the mechanism when
restore_keyboards was written — reasonable, but unmeasured, and this session
has already shown what unmeasured reasoning about this watcher is worth.
It holds: without that call the undock's escalation would have silently
broken the layout of every keyboard that outlives the cable, trading a black
panel for a keyboard that types the wrong characters at the password prompt.

Verified V2 again after the comment/doc edits: nix flake check --no-build,
checks.docking-ux, shellcheck clean.

Round 8 now asks only for what is still open: relogin (the watcher calls the
transition by baked store path, so exec-once means it runs the old build
until then) and repetition — 5+ unplugs, one with the lid shut.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

modules/home/hyprland.nix

@@ -170,10 +170,13 @@ let
     }
     # `hyprctl reload` re-reads the config, and every runtime keyword dies
     # with it — including the `device[<name>]:kb_layout` the keyboard watcher
-    # applies to an external board.  The remembered choices live in the
-    # in-flake state, so `restore` is authoritative and cheap; without this a
-    # reload would silently drop an external keyboard back to the session
-    # layout mid-undock.
+    # applies to an external board.  Measured on hardware 2026-07-14: a bare
+    # reload took a keyboard remembered as `us` straight back to the session's
+    # `gb`, so without this the undock's escalation would silently break the
+    # layout of any keyboard that stays behind when the dock leaves (a
+    # wireless receiver in the laptop; only boards on the dock's own hub are
+    # unaffected, and only because they leave with it).  The remembered
+    # choices live in the in-flake state, so `restore` is authoritative.
     restore_keyboards() {
       hyprctl devices -j 2>/dev/null | jq -r '.keyboards[].name' 2>/dev/null \
         | while IFS= read -r kb; do