feat: Add dynamic category system for attribute analysis

Backend:
- Add CategoryMode enum with 4 modes (fixed_only, fixed_plus_custom, custom_only, dynamic_auto)
- Add Step 0 for LLM category analysis before attribute generation
- Implement dynamic prompts for Step 1/2 that work with N categories
- Add execute_step0(), resolve_final_categories(), assemble_dynamic_attribute_tree()
- Update SSE events to include step0_start, step0_complete, categories_resolved

Frontend:
- Add CategorySelector component with mode selection, custom category input, and category count slider
- Update types with CategoryDefinition, Step0Result, DynamicStep1Result, DynamicCausalChain
- Update api.ts with new SSE event handlers
- Update useAttribute hook with category parameters
- Integrate CategorySelector into InputPanel
- Fix mindmap to dynamically extract and display N categories (was hardcoded to 4)
- Add CSS styles for depth 5-8 to support more category levels

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

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

frontend/src/services/api.ts

@@ -3,17 +3,24 @@ import type {
   StreamAnalyzeRequest,
   StreamAnalyzeResponse,
   Step1Result,
-  CausalChain
+  CausalChain,
+  Step0Result,
+  CategoryDefinition,
+  DynamicStep1Result,
+  DynamicCausalChain
 } from '../types';
 
 // 自動使用當前瀏覽器的 hostname，支援遠端存取
 const API_BASE_URL = `http://${window.location.hostname}:8000/api`;
 
 export interface SSECallbacks {
+  onStep0Start?: () => void;
+  onStep0Complete?: (result: Step0Result) => void;
+  onCategoriesResolved?: (categories: CategoryDefinition[]) => void;
   onStep1Start?: () => void;
-  onStep1Complete?: (result: Step1Result) => void;
+  onStep1Complete?: (result: Step1Result | DynamicStep1Result) => void;
   onChainStart?: (index: number, total: number) => void;
-  onChainComplete?: (index: number, chain: CausalChain) => void;
+  onChainComplete?: (index: number, chain: CausalChain | DynamicCausalChain) => void;
   onChainError?: (index: number, error: string) => void;
   onDone?: (response: StreamAnalyzeResponse) => void;
   onError?: (error: string) => void;
@@ -65,6 +72,15 @@ export async function analyzeAttributesStream(
           const eventData = JSON.parse(dataMatch[1]);
 
           switch (eventType) {
+            case 'step0_start':
+              callbacks.onStep0Start?.();
+              break;
+            case 'step0_complete':
+              callbacks.onStep0Complete?.(eventData.result);
+              break;
+            case 'categories_resolved':
+              callbacks.onCategoriesResolved?.(eventData.categories);
+              break;
             case 'step1_start':
               callbacks.onStep1Start?.();
               break;