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/IdeaNode.tsx

@@ -0,0 +1,25 @@
+'use client';
+
+import { NodeProps } from '@xyflow/react';
+import { BaseNode, BaseNodeData } from './BaseNode';
+
+export function IdeaNode(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="M13 10V3L4 14h7v7l9-11h-7z"
+          />
+        </svg>
+      }
+      color="#f59e0b"
+      borderStyle="dashed"
+    />
+  );
+}