fix(waybar): drop the bar to the bottom layer so fullscreen covers it

On Hyprland the `top` layer renders above every window, including a real
fullscreen surface — so a browser video gone fullscreen sat *under* the
bar (BACKLOG item 30). Move the bar to `layer: bottom` in the generated
waybar.nix and all four whole-swap jsoncs (parity rule); the exclusive
zone still reserves its space in normal tiling, but a fullscreen window
now covers it. Rationale comment kept in waybar.nix; data jsoncs left
comment-free (they carry none).

Verified: V0 (nix flake check --no-build, green) + V1
(homeConfigurations.nomarchy.activationPackage builds; built
.config/waybar/config shows "layer": "bottom"). V3 queued in
HARDWARE-QUEUE (fullscreen covers bar + returns on exit; floating-overlap
trade-off).

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

themes/boreal/waybar.jsonc

@@ -4,7 +4,7 @@
   "margin-right": 14,
   "margin-bottom": 0,
   "height": 38,
-  "layer": "top",
+  "layer": "bottom",
   "position": "top",
   "spacing": 4,
   "reload_style_on_change": true,

themes/executive-slate/waybar.jsonc

@@ -4,7 +4,7 @@
   "margin-bottom": 0,
   "margin-right": 0,
   "height": 34,
-  "layer": "top",
+  "layer": "bottom",
   "position": "top",
   "spacing": 0,
   "reload_style_on_change": true,

themes/summer-day/waybar.jsonc

@@ -4,7 +4,7 @@
   "margin-bottom": 0,
   "margin-right": 120,
   "height": 60,
-  "layer": "top",
+  "layer": "bottom",
   "position": "top",
   "spacing": 15,
   "reload_style_on_change": true,

themes/summer-night/waybar.jsonc

@@ -4,7 +4,7 @@
   "margin-bottom": 0,
   "margin-right": 120,
   "height": 61,
-  "layer": "top",
+  "layer": "bottom",
   "position": "top",
   "spacing": 15,
   "reload_style_on_change": true,