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.

home/system/caelestia-shell/appearance.nix

@@ -0,0 +1,50 @@
+{
+  pkgs,
+  config,
+  ...
+}: let
+  inherit (config.theme) bar-rounding bar-thickness;
+  inherit (config.stylix) fonts;
+in {
+  home.packages = with pkgs; [
+    papirus-icon-theme
+  ];
+
+  programs.caelestia.settings = {
+    paths.sessionGif = ./session-gif-hacker-cat.gif;
+    background.enabled = false;
+    appearance = {
+      transparency = {
+        enabled = true;
+        base = config.theme.active-opacity;
+        layers = config.theme.inactive-opacity;
+      };
+      font.family = {
+        material = "Material Symbols Rounded";
+        mono = fonts.monospace.name;
+        sans = fonts.sansSerif.name;
+      };
+    };
+    utilities = {
+      enabled = true;
+      maxToasts = 4;
+      toasts = {
+        audioInputChanged = false;
+        audioOutputChanged = false;
+        capsLockChanged = false;
+        chargingChanged = true;
+        configLoaded = false;
+        dndChanged = true;
+        gameModeChanged = true;
+        numLockChanged = false;
+        nowPlaying = false;
+        kbLayoutChanged = false;
+      };
+    };
+    dashboard.showOnHover = false;
+    border = {
+      rounding = bar-rounding;
+      thickness = bar-thickness;
+    };
+  };
+}