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/knowledge/StatsDashboard.tsx

@@ -37,13 +37,13 @@ interface KnowledgeStats {
   }[];
 }
 
-export function StatsDashboard() {
+export function StatsDashboard(): React.JSX.Element {
   const [stats, setStats] = useState<KnowledgeStats | null>(null);
   const [isLoading, setIsLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
 
   useEffect(() => {
-    async function loadStats() {
+    async function loadStats(): Promise<void> {
       try {
         setIsLoading(true);
         const data = await fetchKnowledgeStats();
@@ -91,7 +91,7 @@ export function StatsDashboard() {
         <StatsCard
           title="Total Entries"
           value={overview.totalEntries}
-          subtitle={`${overview.publishedEntries} published • ${overview.draftEntries} drafts`}
+          subtitle={`${String(overview.publishedEntries)} published • ${String(overview.draftEntries)} drafts`}
           icon="📚"
         />
         <StatsCard
@@ -229,7 +229,7 @@ function StatsCard({
   value: number;
   subtitle: string;
   icon: string;
-}) {
+}): React.JSX.Element {
   return (
     <div className="bg-white dark:bg-gray-800 rounded-lg shadow p-6">
       <div className="flex items-center justify-between">