theme: calm YoRHa lock screen and power menu; nvim and btop follow

The lock screen and the power menu lose the last Persona motion: no split
display type, no grid sweeping in behind a dark column, no tilted slabs, no
skewed password blocks or hard shake. Both are now one small group of type in
the dark — the porthole mark, a line of light display type, a status line, and
either a rounded password field that fills with dots or a NieR menu whose
selected row is a pill of light (rust for the session-ending three). The lock
keeps the wallpaper almost whole; a wrong password nudges the field once and
turns it to rust. P5Backdrop and the grid texture had no users left and go.

Neovim moves to a local yorha colorscheme (nvim submodule) and btop gets a
yorha theme with hairline boxes and grey-to-light gradients.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

quickshell/config/Theme.qml

@@ -240,10 +240,8 @@ Singleton {
     readonly property var easeIn: [0.55, 0.0, 0.9, 0.35, 1, 1]
 
     // -------------------------------------------------------------- textures
-    // A 1px dot every 8px, and a 32px hairline grid — the two backgrounds the
-    // NieR menus are printed on.
+    // A 1px dot every 8px, the ground NieR's menus are printed on.
     readonly property url texDots: "root:/assets/dots.png"
-    readonly property url texGrid: "root:/assets/grid.png"
     readonly property url texScanline: "root:/assets/scanline.png"
 
     // Last resort only. The live wallpaper comes from the Wallpaper singleton,