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/components/mindmap/hooks/useGraphData.ts

@@ -284,7 +284,7 @@ export function useGraphData(options: UseGraphDataOptions = {}): UseGraphDataRes
   }, [accessToken]);
 
   const fetchMermaid = useCallback(
-    (style: "flowchart" | "mindmap" = "flowchart"): void => {
+    async (style: "flowchart" | "mindmap" = "flowchart"): Promise<void> => {
       if (!graph) {
         setError("No graph data available");
         return;
@@ -356,7 +356,7 @@ export function useGraphData(options: UseGraphDataOptions = {}): UseGraphDataRes
     [graph]
   );
 
-  const fetchStatistics = useCallback((): void => {
+  const fetchStatistics = useCallback(async (): Promise<void> => {
     if (!graph) return;
 
     try {
@@ -577,7 +577,7 @@ export function useGraphData(options: UseGraphDataOptions = {}): UseGraphDataRes
   // Update statistics when graph changes
   useEffect(() => {
     if (graph) {
-      void fetchStatistics();
+      fetchStatistics();
     }
   }, [graph, fetchStatistics]);