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.

server-modules/kernel-hardening.nix

@@ -0,0 +1,35 @@
+# Kernel hardening for the server
+{
+  boot.kernel.sysctl = {
+    # Restrict access to kernel logs and pointers
+    "kernel.dmesg_restrict" = 1;
+    "kernel.kptr_restrict" = 2;
+
+    # BPF hardening
+    "net.core.bpf_jit_harden" = 2;
+    "kernel.unprivileged_bpf_disabled" = 1;
+
+    # Reverse path filtering (anti-spoofing)
+    "net.ipv4.conf.all.rp_filter" = 1;
+    "net.ipv4.conf.default.rp_filter" = 1;
+
+    # SYN flood protection
+    "net.ipv4.tcp_syncookies" = 1;
+
+    # Disable IP source routing
+    "net.ipv4.conf.all.accept_source_route" = 0;
+    "net.ipv4.conf.default.accept_source_route" = 0;
+
+    # Ignore ICMP redirects (prevent MITM)
+    "net.ipv4.conf.all.accept_redirects" = 0;
+    "net.ipv4.conf.default.accept_redirects" = 0;
+    "net.ipv4.conf.all.secure_redirects" = 0;
+    "net.ipv6.conf.all.accept_redirects" = 0;
+
+    # Don't send ICMP redirects
+    "net.ipv4.conf.all.send_redirects" = 0;
+
+    # Restrict ptrace to parent processes only
+    "kernel.yama.ptrace_scope" = 1;
+  };
+}