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/layout/Navigation.tsx

@@ -5,7 +5,7 @@ import Link from "next/link";
 import { useAuth } from "@/lib/auth/auth-context";
 import { LogoutButton } from "@/components/auth/LogoutButton";
 
-export function Navigation() {
+export function Navigation(): React.JSX.Element {
   const pathname = usePathname();
   const { user } = useAuth();
 

apps/web/src/components/layout/ThemeToggle.tsx

@@ -6,7 +6,7 @@ interface ThemeToggleProps {
   className?: string;
 }
 
-export function ThemeToggle({ className = "" }: ThemeToggleProps) {
+export function ThemeToggle({ className = "" }: ThemeToggleProps): React.JSX.Element {
   const { resolvedTheme, toggleTheme } = useTheme();
 
   return (