fix: Resolve all ESLint errors and warnings in web package

Fixes all 542 ESLint problems in the web package to achieve 0 errors and 0 warnings.

Changes:
- Fixed 144 issues: nullish coalescing, return types, unused variables
- Fixed 118 issues: unnecessary conditions, type safety, template literals
- Fixed 79 issues: non-null assertions, unsafe assignments, empty functions
- Fixed 67 issues: explicit return types, promise handling, enum comparisons
- Fixed 45 final warnings: missing return types, optional chains
- Fixed 25 typecheck-related issues: async/await, type assertions, formatting
- Fixed JSX.Element namespace errors across 90+ files

All Quality Rails violations resolved. Lint and typecheck both pass with 0 problems.

Files modified: 118 components, tests, hooks, and utilities

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

apps/web/src/components/calendar/Calendar.tsx

@@ -7,7 +7,7 @@ interface CalendarProps {
   isLoading: boolean;
 }
 
-export function Calendar({ events, isLoading }: CalendarProps) {
+export function Calendar({ events, isLoading }: CalendarProps): React.JSX.Element {
   if (isLoading) {
     return (
       <div className="flex justify-center items-center p-8">
@@ -29,9 +29,7 @@ export function Calendar({ events, isLoading }: CalendarProps) {
   // Group events by date
   const groupedEvents = events.reduce<Record<string, Event[]>>((groups, event) => {
     const label = getDateGroupLabel(event.startTime);
-    if (!groups[label]) {
-      groups[label] = [];
-    }
+    groups[label] ??= [] as Event[];
     groups[label].push(event);
     return groups;
   }, {});

apps/web/src/components/calendar/EventCard.tsx

@@ -5,7 +5,7 @@ interface EventCardProps {
   event: Event;
 }
 
-export function EventCard({ event }: EventCardProps) {
+export function EventCard({ event }: EventCardProps): React.JSX.Element {
   return (
     <div className="bg-white p-3 rounded-lg border-l-4 border-blue-500 shadow-sm hover:shadow-md transition-shadow">
       <div className="flex justify-between items-start mb-1">