Initial import of HortusFox Nix flake packaging

Packages HortusFox from source via php.buildComposerProject and provides
a NixOS module (services.hortusfox-web) to deploy it as a full service
(mariadb + phpfpm + nginx/caddy + ACME + cron timers).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.editorconfig

@@ -0,0 +1,15 @@
+# EditorConfig is awesome: https://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+# Unix-style newlines with a newline ending every file
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+# nix files
+[*.nix]
+indent_style = space
+indent_size = 2
+