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/providers/ThemeProvider.tsx

@@ -92,8 +92,12 @@ export function ThemeProvider({ children, defaultTheme = "system" }: ThemeProvid
         value={{
           theme: defaultTheme,
           resolvedTheme: "dark",
-          setTheme: (): void => {},
-          toggleTheme: (): void => {},
+          setTheme: (): void => {
+            // No-op during SSR
+          },
+          toggleTheme: (): void => {
+            // No-op during SSR
+          },
         }}
       >
         {children}