fix(CQ-WEB-11+12): Fix accessibility labels + SSR window check

CQ-WEB-11: Add aria-label attributes to search input, date inputs,
and id/htmlFor associations for status and priority filter checkboxes
in FilterBar component to improve screen reader accessibility.

CQ-WEB-12: Guard all browser-specific API usage in ReactFlowEditor
behind typeof window checks. Move isDark detection into useState +
useEffect to prevent SSR/hydration mismatches.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/components/mindmap/ReactFlowEditor.tsx

@@ -222,7 +222,9 @@ export function ReactFlowEditor({
   }, [readOnly, selectedNode, onNodeDelete, setNodes, setEdges]);
 
   // Keyboard shortcuts
-  useEffect((): (() => void) => {
+  useEffect((): (() => void) | undefined => {
+    if (typeof window === "undefined") return undefined;
+
     const handleKeyDown = (event: KeyboardEvent): void => {
       if (readOnly) return;
 
@@ -240,8 +242,13 @@ export function ReactFlowEditor({
     };
   }, [readOnly, selectedNode, handleDeleteSelected]);
 
-  const isDark =
-    typeof window !== "undefined" && document.documentElement.classList.contains("dark");
+  // Dark mode detection - must be in state+effect to avoid SSR/hydration mismatch
+  const [isDark, setIsDark] = useState(false);
+  useEffect((): void => {
+    if (typeof window !== "undefined") {
+      setIsDark(document.documentElement.classList.contains("dark"));
+    }
+  }, []);
 
   return (
     <div className={`w-full h-full ${className}`} style={{ minHeight: "500px" }}>