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>

plugins/two-factor-auth/js/TwoFactorAuthLogin.js

@@ -25,7 +25,7 @@
 		}
 	});
 
-	// https://github.com/nextgen-networks/snappymail/issues/349
+	// https://github.com/the-djmaze/snappymail/issues/349
 	addEventListener('sm-show-screen', e => {
 		if (!e.detail.startsWith('settings') && rl.settings.get('SetupTwoFactor')) {
 			e.preventDefault();