fix(06): IN-05 extract duplicated dialog focus-trap into shared useFocusTrap hook

apps/pwa/src/hooks/useFocusTrap.ts

@@ -0,0 +1,50 @@
+/**
+ * useFocusTrap — Tab / Shift+Tab focus cycling within a dialog (IN-05).
+ *
+ * Extracted from the verbatim-duplicated handleDialogKeyDown in EventForm.tsx and
+ * SeriesEditPrompt.tsx so a future fix (handling disabled/hidden elements, radio-group
+ * focus, etc.) lands in one place.
+ *
+ * Returns a keydown handler to spread onto the dialog container's `onKeyDown`. The
+ * handler queries the dialog's focusable descendants on each keydown:
+ *   - Tab on the last focusable element wraps to the first.
+ *   - Shift+Tab on the first focusable element wraps to the last.
+ *
+ * No external library — keeps the zero-dependency posture of the original inline impl.
+ *
+ * @param dialogRef - ref to the dialog container element
+ */
+import type { KeyboardEvent, RefObject } from 'react'
+
+export function useFocusTrap(
+  dialogRef: RefObject<HTMLDivElement | null>,
+): (e: KeyboardEvent<HTMLDivElement>) => void {
+  return (e: KeyboardEvent<HTMLDivElement>) => {
+    if (e.key !== 'Tab' || !dialogRef.current) return
+
+    const focusable = Array.from(
+      dialogRef.current.querySelectorAll<HTMLElement>(
+        'button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])',
+      ),
+    ).filter((el) => !el.hasAttribute('disabled') && el.getAttribute('tabindex') !== '-1')
+
+    if (focusable.length === 0) return
+
+    const first = focusable[0]
+    const last = focusable[focusable.length - 1]
+
+    if (e.shiftKey) {
+      // Shift+Tab: if on first element, wrap to last
+      if (document.activeElement === first) {
+        e.preventDefault()
+        last.focus()
+      }
+    } else {
+      // Tab: if on last element, wrap to first
+      if (document.activeElement === last) {
+        e.preventDefault()
+        first.focus()
+      }
+    }
+  }
+}