Add new server modules and configurations for various services

- Introduced `default-creds` module for managing default credentials with Umami integration.
- Added `fail2ban` module for brute-force attack protection with configurable ban times.
- Created `firewall` module to enable and configure basic firewall settings.
- Implemented `gitea` module for self-hosted Git service with PostgreSQL backend.
- Developed `glance` module for a customizable dashboard with various widgets and themes.
- Added `iknowyou` module for a self-hosted password manager with production and demo environments.
- Introduced `kernel-hardening` module for enhancing kernel security settings.
- Created `mazanoke` module for a simple web application with Nginx integration.
- Added `mealie` module for a self-hosted meal planning application.
- Implemented `stirling-pdf` module for PDF generation service.
- Developed `umami` module for self-hosted analytics with secret management.
- Added `ssh` module for secure SSH configuration with user restrictions.
- Introduced `nixy` theme for a customized aesthetic experience across services.

docs/GROUPS.md

@@ -0,0 +1,44 @@
+# Groups
+
+Groups are curated sets of packages exposed as flake outputs. Each group has two forms:
+
+- **`homeManagerModules.<group>`** — full home-manager module (packages + files + systemd units)
+- **`packages.<group>`** — standalone environment for `nix shell` (packages only)
+
+## Available groups
+
+- dev (go, bun, air, ...)
+- cybersecurity (nmap, john, dirb, ffuf, ...)
+
+For the Cybersecurity group, the home-manager module also sets up:
+
+- `~/Cyber/wordlists/` with SecLists, fuzz4bounty, and hashcat rules
+- `~/Cyber/tmp/` as a temporary workspace
+
+## Use in another flake
+
+Add this repo as an input:
+
+```nix
+inputs.nixy.url = "github:anotherhadi/nixy";
+```
+
+Import the home-manager module in your home configuration:
+
+```nix
+{ inputs, ... }: {
+  imports = [
+    inputs.nixy.homeManagerModules.cybersecurity
+    # inputs.nixy.homeManagerModules.dev
+  ];
+}
+```
+
+## Quick shell without installing
+
+```sh
+nix shell github:anotherhadi/nixy#cybersecurity
+nix shell github:anotherhadi/nixy#dev
+```
+
+This drops you into a shell with all tools in `PATH`. No home-manager required, no wordlists or systemd units.