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/nextcloud/js/composer.js

@@ -35,7 +35,7 @@
 					});
 					if (urls.length) {
 						// TODO: other editors and text/plain
-						// https://github.com/nextgen-networks/snappymail/issues/981
+						// https://github.com/the-djmaze/snappymail/issues/981
 						view.oEditor.editor.squire.insertHTML(urls.join("<br>"));
 					}
 				});

plugins/nextcloud/js/message.js

@@ -27,7 +27,7 @@
 				}
 			}
 /*
-			// https://github.com/nextgen-networks/snappymail/issues/592
+			// https://github.com/the-djmaze/snappymail/issues/592
 			if (cfg.CalDAV) {
 				const attachmentsPlace = template.content.querySelector('.attachmentsPlace');
 				attachmentsPlace.after(Element.fromHTML(`

plugins/nextcloud/js/webdav.js

@@ -113,7 +113,7 @@ const
 				}
 				elemList.push(elem);
 			}
-			// https://github.com/nextgen-networks/snappymail/issues/1177
+			// https://github.com/the-djmaze/snappymail/issues/1177
 //			elemList.sort((a, b) => a.isFile != b.isFile ? (a.isFile ? 1 : -1) : a.name.localeCompare(b.name));
 			return Promise.resolve(elemList);
 		});
@@ -122,7 +122,7 @@ const
 	buildTree = (view, parent, items, path) => {
 		if (items.length) {
 			try {
-				// https://github.com/nextgen-networks/snappymail/issues/1109
+				// https://github.com/the-djmaze/snappymail/issues/1109
 				let collator = new Intl.Collator(undefined, {numeric: true, sensitivity: 'base'});
 				items.sort((a, b) => collator.compare(a.name, b.name));
 			} catch (e) {