Rebrand to new MediaManager logo (#452)

I made two new logos because the old one wasn't very recognizable at a
glance.


![1](https://github.com/user-attachments/assets/cb37a709-e80b-4c97-a4d8-cf9ba0dc1613)

![3](https://github.com/user-attachments/assets/c56ded5c-fe15-4c02-bc20-fe2bff06caf9)

mkdocs.yml

@@ -2,7 +2,7 @@ site_name: "MediaManager Documentation"
 theme:
   name: "material"
   logo: "assets/logo.svg"
-  favicon: "assets/logo.svg"
+  favicon: "assets/favicon.ico"
   features:
     - navigation.sections
     - navigation.expand
@@ -68,3 +68,5 @@ nav:
 extra:
   version:
     provider: mike
+extra_css:
+  - custom.css