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/app/demo/kanban/page.tsx

@@ -157,7 +157,7 @@ const initialTasks: Task[] = [
 export default function KanbanDemoPage(): ReactElement {
   const [tasks, setTasks] = useState<Task[]>(initialTasks);
 
-  const handleStatusChange = (taskId: string, newStatus: TaskStatus) => {
+  const handleStatusChange = (taskId: string, newStatus: TaskStatus): void => {
     setTasks((prevTasks) =>
       prevTasks.map((task) =>
         task.id === taskId