refactor : rename Inventory_frontend to frontend everywhere

Update Dockerfile, nginx, .dockerignore, makefile, CI workflow,
CLAUDE.md, README, release script to use frontend/ instead of
Inventory_frontend/. Remove submodule references from CI and
release script.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/docker/nginx.conf

@@ -2,7 +2,7 @@ server {
     listen 80;
     server_name _;
 
-    root /var/www/html/Inventory_frontend/.output/public;
+    root /var/www/html/frontend/.output/public;
     index index.html;
 
     access_log /dev/stdout;