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/(auth)/callback/page.test.tsx

@@ -7,11 +7,11 @@ const mockPush = vi.fn();
 const mockSearchParams = new Map<string, string>();
 
 vi.mock("next/navigation", () => ({
-  useRouter: () => ({
+  useRouter: (): { push: typeof mockPush } => ({
     push: mockPush,
   }),
-  useSearchParams: () => ({
-    get: (key: string) => mockSearchParams.get(key),
+  useSearchParams: (): { get: (key: string) => string | undefined } => ({
+    get: (key: string): string | undefined => mockSearchParams.get(key),
   }),
 }));