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/app/utils/events.ts

@@ -0,0 +1,41 @@
+/**
+ * Type-safe event handlers for form inputs.
+ * These helpers extract values from DOM events in a way that satisfies TypeScript.
+ */
+
+/**
+ * Extract the string value from an input event.
+ */
+export const getInputValue = (event: Event): string => {
+  const target = event.target as HTMLInputElement | null
+  return target?.value ?? ''
+}
+
+/**
+ * Extract the numeric value from an input event.
+ */
+export const getInputNumber = (event: Event): number => {
+  const target = event.target as HTMLInputElement | null
+  const value = target?.value ?? ''
+  const parsed = parseFloat(value)
+  return Number.isNaN(parsed) ? 0 : parsed
+}
+
+/**
+ * Extract the checked state from a checkbox event.
+ */
+export const getCheckboxValue = (event: Event): boolean => {
+  const target = event.target as HTMLInputElement | null
+  return target?.checked ?? false
+}
+
+/**
+ * Extract an optional numeric value from an input event (empty string = undefined).
+ */
+export const getOptionalNumber = (event: Event): number | undefined => {
+  const target = event.target as HTMLInputElement | null
+  const value = target?.value ?? ''
+  if (value.trim() === '') return undefined
+  const parsed = parseFloat(value)
+  return Number.isNaN(parsed) ? undefined : parsed
+}