tirith: add module

Adds Home Manager module for Tirith, a shell security monitor.

The module supports:
- Shell integration for Bash, Fish, and Zsh
- Allowlist configuration for bypassing Tirith analysis
- Policy configuration for customizing security behavior

modules/misc/news/2026/02/2026-02-13_12-21-10.nix

@@ -0,0 +1,11 @@
+{
+  time = "2026-02-13T11:21:10+00:00";
+  condition = true;
+  message = ''
+
+    A new module is available: 'programs.tirith'.
+
+    Tirith is a shell security monitor that helps protect against
+    malicious commands by analyzing shell inputs before execution.
+  '';
+}