feat: Add Expert Transformation Agent with multi-expert perspective system

- Backend: Add expert transformation router with 3-step SSE pipeline
  - Step 0: Generate diverse expert team (random domains)
  - Step 1: Each expert generates keywords for attributes
  - Step 2: Batch generate descriptions for expert keywords
- Backend: Add simplified prompts for reliable JSON output
- Frontend: Add TransformationPanel with React Flow visualization
- Frontend: Add TransformationInputPanel for expert configuration
  - Expert count (2-8), keywords per expert (1-3)
  - Custom expert domains support
- Frontend: Add expert keyword nodes with expert badges
- Frontend: Improve description card layout (wider cards, more spacing)
- Frontend: Add fallback for missing descriptions with visual indicators

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/components/dag/useDAGLayout.ts

@@ -50,9 +50,6 @@ export function useDAGLayout(
     const nodes: Node[] = [];
     const sortedCategories = [...data.categories].sort((a, b) => a.order - b.order);
 
-    // Unified column spacing
-    const columnGap = 60; // Consistent gap between ALL adjacent elements
-
     // Build category color map
     const categoryColors: Record<string, { fill: string; stroke: string }> = {};
     sortedCategories.forEach((cat, index) => {