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/dashboard/DomainOverviewWidget.tsx

@@ -6,7 +6,10 @@ interface DomainOverviewWidgetProps {
   isLoading: boolean;
 }
 
-export function DomainOverviewWidget({ tasks, isLoading }: DomainOverviewWidgetProps) {
+export function DomainOverviewWidget({
+  tasks,
+  isLoading,
+}: DomainOverviewWidgetProps): React.JSX.Element {
   if (isLoading) {
     return (
       <div className="bg-white rounded-lg shadow-sm border border-gray-200 p-6">
@@ -25,7 +28,15 @@ export function DomainOverviewWidget({ tasks, isLoading }: DomainOverviewWidgetP
     highPriority: tasks.filter((t) => t.priority === TaskPriority.HIGH).length,
   };
 
-  const StatCard = ({ label, value, color }: { label: string; value: number; color: string }) => (
+  const StatCard = ({
+    label,
+    value,
+    color,
+  }: {
+    label: string;
+    value: number;
+    color: string;
+  }): React.JSX.Element => (
     <div className={`p-4 rounded-lg bg-gradient-to-br ${color}`}>
       <div className="text-3xl font-bold text-white mb-1">{value}</div>
       <div className="text-sm text-white/90">{label}</div>

apps/web/src/components/dashboard/QuickCaptureWidget.tsx

@@ -4,11 +4,11 @@ import { useState } from "react";
 import { Button } from "@mosaic/ui";
 import { useRouter } from "next/navigation";
 
-export function QuickCaptureWidget() {
+export function QuickCaptureWidget(): React.JSX.Element {
   const [idea, setIdea] = useState("");
   const router = useRouter();
 
-  const handleSubmit = (e: React.SyntheticEvent<HTMLFormElement>) => {
+  const handleSubmit = (e: React.SyntheticEvent<HTMLFormElement>): void => {
     e.preventDefault();
     if (!idea.trim()) return;
 
@@ -18,7 +18,7 @@ export function QuickCaptureWidget() {
     setIdea("");
   };
 
-  const goToTasks = () => {
+  const goToTasks = (): void => {
     router.push("/tasks");
   };
 

apps/web/src/components/dashboard/RecentTasksWidget.tsx

@@ -17,7 +17,7 @@ const statusIcons: Record<TaskStatus, string> = {
   [TaskStatus.ARCHIVED]: "💤",
 };
 
-export function RecentTasksWidget({ tasks, isLoading }: RecentTasksWidgetProps) {
+export function RecentTasksWidget({ tasks, isLoading }: RecentTasksWidgetProps): React.JSX.Element {
   if (isLoading) {
     return (
       <div className="bg-white rounded-lg shadow-sm border border-gray-200 p-6">

apps/web/src/components/dashboard/UpcomingEventsWidget.tsx

@@ -7,7 +7,10 @@ interface UpcomingEventsWidgetProps {
   isLoading: boolean;
 }
 
-export function UpcomingEventsWidget({ events, isLoading }: UpcomingEventsWidgetProps) {
+export function UpcomingEventsWidget({
+  events,
+  isLoading,
+}: UpcomingEventsWidgetProps): React.JSX.Element {
   if (isLoading) {
     return (
       <div className="bg-white rounded-lg shadow-sm border border-gray-200 p-6">