refactor : merge Inventory_frontend submodule into frontend/ directory

Merges the full git history of Inventory_frontend into the monorepo
under frontend/. Removes the submodule in favor of a unified repo.

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

frontend/.gitignore

@@ -0,0 +1,29 @@
+# Nuxt dev/build outputs
+.output
+.data
+.nuxt
+.nitro
+.cache
+dist
+
+# Node dependencies
+node_modules
+
+# Logs
+logs
+*.log
+
+# Misc
+.DS_Store
+.fleet
+.idea
+
+# Local env files
+.env
+.env.*
+!.env.example
+
+# Playwright
+e2e/.auth/
+playwright-report/
+test-results/