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/page.test.tsx

@@ -5,7 +5,11 @@ import Home from "./page";
 // Mock Next.js navigation
 const mockPush = vi.fn();
 vi.mock("next/navigation", () => ({
-  useRouter: () => ({
+  useRouter: (): {
+    push: typeof mockPush;
+    replace: ReturnType<typeof vi.fn>;
+    prefetch: ReturnType<typeof vi.fn>;
+  } => ({
     push: mockPush,
     replace: vi.fn(),
     prefetch: vi.fn(),
@@ -14,7 +18,13 @@ vi.mock("next/navigation", () => ({
 
 // Mock auth context
 vi.mock("@/lib/auth/auth-context", () => ({
-  useAuth: () => ({
+  useAuth: (): {
+    user: null;
+    isLoading: boolean;
+    isAuthenticated: boolean;
+    signOut: ReturnType<typeof vi.fn>;
+    refreshSession: ReturnType<typeof vi.fn>;
+  } => ({
     user: null,
     isLoading: false,
     isAuthenticated: false,