feat(fe): Add form field navigation - Enter key moves to next field

- Create useFormFieldNavigation composable for Tab-like Enter behavior
- KsTextField: Enter -> next field
- KsTextArea: Ctrl+Enter for newline, Enter -> next field
- KsSelect: Enter -> next field after selection
- Implements standard form navigation pattern across input components

frontend/src/shared/ui/composables/useFormFieldNavigation.ts

@@ -0,0 +1,91 @@
+import { ref, onMounted } from 'vue'
+
+export function useFormFieldNavigation() {
+  const inputRef = ref<HTMLElement | null>(null)
+
+  function findFormElement(): HTMLFormElement | null {
+    if (!inputRef.value) return null
+    return inputRef.value.closest('form')
+  }
+
+  function getFormInputElements(): HTMLElement[] {
+    const form = findFormElement()
+    if (!form) return []
+
+    const selectors = [
+      'input:not([type="hidden"]):not([type="checkbox"]):not([type="radio"])',
+      'textarea',
+      '[role="button"][tabindex="0"]',
+      'select'
+    ]
+
+    return Array.from(form.querySelectorAll(selectors.join(',')))
+      .filter((el: Element): el is HTMLElement => {
+        if (el instanceof HTMLInputElement) {
+          return !el.disabled && !el.readonly && el.type !== 'hidden'
+        }
+        if (el instanceof HTMLTextAreaElement) {
+          return !el.disabled && !el.readonly
+        }
+        if (el instanceof HTMLSelectElement) {
+          return !el.disabled && !el.readonly
+        }
+        return !el.hasAttribute('disabled')
+      })
+  }
+
+  function findNextField(): HTMLElement | null {
+    const elements = getFormInputElements()
+    if (!inputRef.value || elements.length === 0) return null
+
+    const currentIndex = elements.indexOf(inputRef.value)
+    if (currentIndex === -1) return null
+
+    const nextIndex = currentIndex + 1
+    return nextIndex < elements.length ? elements[nextIndex] : elements[0]
+  }
+
+  function moveToNextField(): void {
+    const nextField = findNextField()
+    if (nextField) {
+      nextField.focus()
+      // 如果是 input/textarea，select all
+      if (nextField instanceof HTMLInputElement || nextField instanceof HTMLTextAreaElement) {
+        nextField.select?.()
+      }
+    }
+  }
+
+  function handleKeyDown(event: KeyboardEvent, isTextArea: boolean = false): boolean {
+    if (!isTextArea) {
+      // Input/Select: Enter → 다음 필드
+      if (event.key === 'Enter') {
+        event.preventDefault()
+        moveToNextField()
+        return true
+      }
+    } else {
+      // TextArea: Ctrl+Enter → 줄바꿈, Enter → 다음 필드
+      if (event.key === 'Enter') {
+        if (event.ctrlKey || event.metaKey) {
+          // Ctrl+Enter: 줄바꿈 (기본 동작)
+          return false
+        } else {
+          // Enter: 다음 필드
+          event.preventDefault()
+          moveToNextField()
+          return true
+        }
+      }
+    }
+    return false
+  }
+
+  return {
+    inputRef,
+    handleKeyDown,
+    moveToNextField,
+    findNextField,
+    getFormInputElements
+  }
+}