feat: add Lotus Chat custom logo across all web app icons

Replaces all PWA, Android, Apple touch, and favicon assets with the
custom Lotus Chat logo (lotus_chat.png, 1254x1254 source).

Adds attribution section to README per CC BY 4.0 requirements:
the logo is a derivative of the original Cinny logo by Ajay Bura,
used under CC BY 4.0, and the modified version is likewise CC BY 4.0.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -6,6 +6,14 @@ A Matrix chat client built for Lotus Guild — fast, private, and packed with th
 
 ---
 
+## Licensing & Attribution
+
+The source code is licensed under [AGPLv3](LICENSE), the same license as the upstream Cinny project. The source for this fork is public at [code.lotusguild.org/LotusGuild/cinny](https://code.lotusguild.org/LotusGuild/cinny).
+
+The Lotus Chat logo (`lotus_chat.png`) is a derivative work based on the original Cinny logo by Ajay Bura and contributors, used under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/). The modified logo is © Lotus Guild and is also made available under CC BY 4.0.
+
+---
+
 ## Features
 
 ### Messaging