feat(pwa): blue splash screen with the logo, status bar follows the theme

Manifest: short name, blue background/theme colour for the Android splash.
index.html shows a plain blue screen with the logo until React mounts.
theme-color starts blue and then follows the active theme background.

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

frontend/public/manifest.json

@@ -1,13 +1,13 @@
 {
   "id": "/",
-  "name": "MindSift — Der Kopf frei in drei Sekunden",
+  "name": "MindSift",
   "short_name": "MindSift",
-  "description": "Instant Brain-Dump, Tinder-Style Triage, Workspace & Echtzeit-Familienlisten.",
+  "description": "MindSift — Der Kopf frei in drei Sekunden. Instant Brain-Dump, Tinder-Style Triage, Workspace & Echtzeit-Familienlisten.",
   "start_url": "/",
   "scope": "/",
   "display": "standalone",
-  "background_color": "#0b0f19",
-  "theme_color": "#0b0f19",
+  "background_color": "#2563eb",
+  "theme_color": "#2563eb",
   "orientation": "portrait-primary",
   "icons": [
     {