feat(sway): 4K scale 2, natural mouse scroll, idle inhibit for emulators

Three unrelated desktop-side fixes, all in home/sway.nix.

Sway cannot key an output rule on resolution, so scale 2 on 4K displays
is applied by a user service that runs once at session start and again on
every output event, which is what makes it survive a display being
switched off and on. The scale guard in the jq filter stops the
subscription feeding itself. kanshi still owns mode and position; no
profile here sets a scale, so the two do not fight.

natural_scroll on type:pointer gives mice the same scroll direction as
the touchpads already had.

PCSX2 and Dolphin default to borderless-windowed rather than compositor
fullscreen, so the existing inhibit_idle fullscreen rules never matched
and swaylock engaged mid-game. Inhibit on focus for the emulators
instead. The Steam session is unaffected either way: swayidle is wanted
by graphical-session.target and conditional on WAYLAND_DISPLAY, and the
gamescope session provides neither.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/keybindings.md

@@ -18,8 +18,8 @@ rebuild, never the generated dotfiles.
 - Letter keys are **keysyms** (the character produced), not physical positions.
   The keyboard is **Dvorak** (`us`/`dvorak`), so e.g. "Super+s" is whatever key
   types `s` in Dvorak.
-- Shortcuts apply to every Sway host (MBP, T400, Mac Pro); brightness keys are
-  laptop-only, as noted.
+- Shortcuts apply to every Sway host (MBP, T400, Mac Pro, Console); brightness
+  keys are laptop-only, as noted.
 
 ---