This replaces the experimental flake-based Nix configuration with
a classic Nix setup (`default.nix`, `shell.nix`, `module.nix`)
per user request.
Changes include:
- Removing `flake.nix`.
- Creating `default.nix` to package the python bridge.
- Creating `shell.nix` for a reproducible development environment.
- Creating `module.nix` for the NixOS systemd service.
- The `module.nix` now uses systemd's `LoadCredential=` to safely
expose the XMPP password to the bridge daemon running as a dynamic
user, resolving permission issues.
- `README.md` instructions have been fully rewritten to focus on classic
Nix usage, answering user questions on secret management and repository
cloning structure.
Co-authored-by: jamessucla <2191476+jamessucla@users.noreply.github.com>
