Update repository URLs to nextgen-networks while preserving deep links

Replaced bare references to the-djmaze/snappymail with nextgen-networks/snappymail/
and updated .git URLs to the new organization.

Per user request:
- README files are excluded.
- URLs with a trailing slash (e.g. issues, pull requests, releases) are
  left pointing to the original repository to preserve historical context.
- Bare web URLs now include the requested trailing slash.
- Existing nextgen-networks bare URLs were updated to include the trailing slash.

Co-authored-by: nextgen-networks <21206978+nextgen-networks@users.noreply.github.com>

dev/Stores/Theme.js

@@ -10,7 +10,7 @@ let __themeTimer = 0;
 export const
 	// Also see Styles/_Values.less @maxMobileWidth
 	isMobile = matchMedia('(max-width: 799px)'),
-	// https://github.com/nextgen-networks/snappymail/issues/1150
+	// https://github.com/the-djmaze/snappymail/issues/1150
 //	isSmall = matchMedia('(max-width: 1400px)'),
 
 	ThemeStore = {