refactor(branding): rename project to LockScreenWallpaper across repo

Standardize branding by renaming Wechselbild to LockScreenWallpaper.
This updates UI strings, configs, and plugin metadata for consistency.

- Rename branding across UI, docs, and config in the repo
- Update Android UI strings and notification titles to LockScreenWallpaper

src-tauri/capabilities/default.json

@@ -1,7 +1,7 @@
 {
   "$schema": "../gen/schemas/desktop-schema.json",
   "identifier": "default",
-  "description": "Standardrechte für Wechselbild",
+  "description": "Standardrechte für LockScreenWallpaper",
   "windows": ["main"],
   "permissions": ["core:default", "wallpaper:default"]
 }