fix(pwa): replace white-glyph PWA icons with dark glyph + match dark deck splash color

The 'random icon' users saw on mobile home screens was the white glyph
icon (logo-light.png clone) rendered on iOS/Android's default light
launcher background — visually invisible. Replaces icon-192x192.png and
icon-512x512.png with the dark glyph (logo-dark.png) so the app icon is
visible on light home screens. Manifest background_color flipped from
#ffffff to #0a0b12 so the PWA splash matches the in-app dark deck theme
instead of flashing white before first paint.

Resolves Task 1 of the mobile-foundations sub-project (deferred 'random
icon' report) — root cause was the PWA install icon, not the in-app
header logo (which was already correct).

Author: itsmeakhil

apps/web/public/icon-192x192.png

@@ -4,7 +4,7 @@
     "description": "A collection of developer tools for everyday use.",
     "start_url": "/",
     "display": "standalone",
-    "background_color": "#ffffff",
+    "background_color": "#0a0b12",
     "icons": [
         {
             "src": "/icon-192x192.png",