feat: add mindmap components from jarvis frontend

- Copied mindmap visualization components (ReactFlow-based interactive graph)
- Added MindmapViewer, ReactFlowEditor, MermaidViewer
- Included all node types: Concept, Task, Idea, Project
- Added controls: NodeCreateModal, ExportButton
- Created mindmap route at /mindmap
- Added useGraphData hook for knowledge graph API
- Copied auth-client and api utilities (dependencies)

Note: Requires better-auth packages to be installed for full compilation

apps/web/src/components/mindmap/nodes/ConceptNode.tsx

@@ -0,0 +1,24 @@
+'use client';
+
+import { NodeProps } from '@xyflow/react';
+import { BaseNode, BaseNodeData } from './BaseNode';
+
+export function ConceptNode(props: NodeProps) {
+  return (
+    <BaseNode
+      {...props}
+      data={props.data as BaseNodeData}
+      icon={
+        <svg className="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+          <path
+            strokeLinecap="round"
+            strokeLinejoin="round"
+            strokeWidth={2}
+            d="M9.663 17h4.673M12 3v1m6.364 1.636l-.707.707M21 12h-1M4 12H3m3.343-5.657l-.707-.707m2.828 9.9a5 5 0 117.072 0l-.548.547A3.374 3.374 0 0014 18.469V19a2 2 0 11-4 0v-.531c0-.895-.356-1.754-.988-2.386l-.548-.547z"
+          />
+        </svg>
+      }
+      color="#6366f1"
+    />
+  );
+}