refactor: code efficiency improvements (Issues #9-13, #15, #17-20)

Backend:
- Extract shared hard-delete authorization utility (#9)
- Extract Prisma include constants per entity (#11)
- Fix N+1 query pattern in events findAll (#12)
- Extract shared date utility functions (#13)
- Move vehicle utilization filtering to DB query (#15)
- Add ParseBooleanPipe for query params
- Add CurrentDriver decorator + ResolveDriverInterceptor (#20)

Frontend:
- Extract shared form utilities (toDatetimeLocal) and enum labels (#17)
- Replace browser confirm() with styled ConfirmModal (#18)
- Add centralized query-keys.ts constants (#19)
- Clean up unused imports, add useMemo where needed (#19)
- Standardize filter button styling across list pages

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/lib/utils.ts

@@ -35,3 +35,18 @@ export function formatTime(date: string | Date, timeZone?: string): string {
     ...(timeZone && { timeZone }),
   });
 }
+
+/**
+ * Convert ISO datetime string to datetime-local input format (YYYY-MM-DDTHH:mm)
+ * Used for populating datetime-local inputs in forms
+ */
+export function toDatetimeLocal(isoString: string | null | undefined): string {
+  if (!isoString) return '';
+  const date = new Date(isoString);
+  const year = date.getFullYear();
+  const month = String(date.getMonth() + 1).padStart(2, '0');
+  const day = String(date.getDate()).padStart(2, '0');
+  const hours = String(date.getHours()).padStart(2, '0');
+  const minutes = String(date.getMinutes()).padStart(2, '0');
+  return `${year}-${month}-${day}T${hours}:${minutes}`;
+}