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/hooks/useFlights.ts

@@ -2,10 +2,11 @@ import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { api } from '@/lib/api';
 import { Flight, FlightBudget } from '@/types';
 import toast from 'react-hot-toast';
+import { queryKeys } from '@/lib/query-keys';
 
 export function useFlights() {
   return useQuery<Flight[]>({
-    queryKey: ['flights'],
+    queryKey: queryKeys.flights.all,
     queryFn: async () => {
       const { data } = await api.get('/flights');
       return data;
@@ -16,7 +17,7 @@ export function useFlights() {
 
 export function useFlightBudget() {
   return useQuery<FlightBudget>({
-    queryKey: ['flights', 'budget'],
+    queryKey: queryKeys.flights.budget,
     queryFn: async () => {
       const { data } = await api.get('/flights/tracking/budget');
       return data;
@@ -34,8 +35,8 @@ export function useRefreshFlight() {
       return data;
     },
     onSuccess: (data) => {
-      queryClient.invalidateQueries({ queryKey: ['flights'] });
-      queryClient.invalidateQueries({ queryKey: ['flights', 'budget'] });
+      queryClient.invalidateQueries({ queryKey: queryKeys.flights.all });
+      queryClient.invalidateQueries({ queryKey: queryKeys.flights.budget });
       const status = data.status || 'unknown';
       toast.success(`Flight updated: ${data.flightNumber} (${status})`);
     },
@@ -54,8 +55,8 @@ export function useRefreshActiveFlights() {
       return data;
     },
     onSuccess: (data) => {
-      queryClient.invalidateQueries({ queryKey: ['flights'] });
-      queryClient.invalidateQueries({ queryKey: ['flights', 'budget'] });
+      queryClient.invalidateQueries({ queryKey: queryKeys.flights.all });
+      queryClient.invalidateQueries({ queryKey: queryKeys.flights.budget });
       toast.success(`Refreshed ${data.refreshed} flights (${data.budgetRemaining} API calls remaining)`);
     },
     onError: (error: any) => {