feat(themes): implement declarative theme file management

- Link active theme files from themes/ directly via Home Manager
- Use 'recursive = true' to allow dynamic templating inside linked directories
- Simplify nomarchy-theme-set to rely on declarative links
- Update template generator to point to the unified theme directory

modules/home/theme-files.nix

@@ -0,0 +1,10 @@
+{ config, ... }:
+
+{
+  xdg.configFile."nomarchy/current/theme" = {
+    source = ../../themes/${config.nomarchy.theme};
+    recursive = true;
+  };
+  
+  xdg.configFile."nomarchy/current/theme.name".text = config.nomarchy.theme;
+}