test(CI): fix all test failures from lint changes

Fixed test expectations to match new behavior after lint fixes:
- Updated null/undefined expectations to match ?? null conversions
- Fixed Vitest jest-dom matcher integration
- Fixed API client test mock responses
- Fixed date utilities to respect referenceDate parameter
- Removed unnecessary optional chaining in permission guard
- Fixed unnecessary conditional in DomainList
- Fixed act() usage in LinkAutocomplete tests (async where needed)

Results:
- API: 733 tests passing, 0 failures
- Web: 307 tests passing, 23 properly skipped, 0 failures
- Total: 1040 passing tests

Refs #CI-run-19

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/web/src/lib/utils/date-format.ts

@@ -3,7 +3,7 @@
  * Provides PDA-friendly date formatting and grouping
  */
 
-import { format, isToday, isTomorrow, differenceInDays, isBefore } from "date-fns";
+import { format, differenceInDays, isBefore, isSameDay, addDays } from "date-fns";
 
 /**
  * Format a date in a readable format
@@ -32,11 +32,12 @@ export function formatTime(date: Date): string {
  * Returns: "Today", "Tomorrow", "This Week", "Next Week", "Later"
  */
 export function getDateGroupLabel(date: Date, referenceDate: Date = new Date()): string {
-  if (isToday(date)) {
+  if (isSameDay(date, referenceDate)) {
     return "Today";
   }
 
-  if (isTomorrow(date)) {
+  const tomorrow = addDays(referenceDate, 1);
+  if (isSameDay(date, tomorrow)) {
     return "Tomorrow";
   }