fix: Resolve web package lint and typecheck errors

Fixes ESLint and TypeScript errors in web package to pass CI checks:

- Fixed all Quality Rails violations (14 explicit any types)
- Fixed deprecated React event types (FormEvent → SyntheticEvent)
- Fixed 26 TypeScript errors (Promise types, test mocks, HTMLElement assertions)
- Added vitest DOM matcher type definitions
- Fixed unused variables and empty functions
- Resolved 43+ additional lint errors

Typecheck: ✅ 0 errors
Lint: 542 remaining (non-blocking in CI)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/web/src/lib/api/client.ts

@@ -40,7 +40,7 @@ export async function apiRequest<T>(endpoint: string, options: RequestInit = {})
       (): ApiError => ({
         code: "UNKNOWN_ERROR",
         message: response.statusText || "An unknown error occurred",
-      }),
+      })
     );
 
     throw new Error(error.message);