Replaced references to https://github.com/the-djmaze/snappymail with
https://github.com/nextgen-networks/snappymail/ across the repository,
excluding README files as requested.
The replacement handles trailing slashes carefully to ensure bare URLs
include the slash while sub-paths (like /issues/ or .git) do not result
in double slashes. Files that already used the new domain were also
updated to ensure consistent trailing slash usage.
Co-authored-by: nextgen-networks <21206978+nextgen-networks@users.noreply.github.com>
