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>

backend/app/prompts/attribute_prompt.py

@@ -1,4 +1,5 @@
-from typing import List, Optional
+from typing import List, Optional, Dict
+import json
 
 DEFAULT_CATEGORIES = ["材料", "功能", "用途", "使用族群", "特性"]
 
@@ -115,3 +116,100 @@ def get_flat_attribute_prompt(query: str, categories: Optional[List[str]] = None
 用戶輸入：{query}"""
 
     return prompt
+
+
+# ===== Dynamic category system prompts =====
+
+def get_step0_category_analysis_prompt(query: str, suggested_count: int = 3) -> str:
+    """Step 0: LLM 分析建議類別"""
+    return f"""/no_think
+分析「{query}」，建議 {suggested_count} 個最適合的屬性類別來描述它。
+
+【常見類別參考】材料、功能、用途、使用族群、特性、形狀、顏色、尺寸、品牌、價格區間
+
+【重要】
+1. 選擇最能描述此物件本質的類別
+2. 類別之間應該有邏輯關係（如：材料→功能→用途）
+3. 不要選擇過於抽象或重複的類別
+
+只回傳 JSON：
+{{
+  "categories": [
+    {{"name": "類別1", "description": "說明1", "order": 0}},
+    {{"name": "類別2", "description": "說明2", "order": 1}}
+  ]
+}}
+
+物件：{query}"""
+
+
+def get_step1_dynamic_attributes_prompt(
+    query: str,
+    categories: List  # List[CategoryDefinition]
+) -> str:
+    """動態 Step 1 - 根據類別列表生成屬性"""
+    # 按 order 排序並構建描述
+    sorted_cats = sorted(categories, key=lambda x: x.order if hasattr(x, 'order') else x.get('order', 0))
+
+    category_desc = "\n".join([
+        f"- {cat.name if hasattr(cat, 'name') else cat['name']}: {cat.description if hasattr(cat, 'description') else cat.get('description', '相關屬性')}"
+        for cat in sorted_cats
+    ])
+
+    category_keys = [cat.name if hasattr(cat, 'name') else cat['name'] for cat in sorted_cats]
+    json_template = {cat: ["屬性1", "屬性2", "屬性3"] for cat in category_keys}
+
+    return f"""/no_think
+分析「{query}」，列出以下類別的屬性。每個類別列出 3-5 個常見屬性。
+
+【類別列表】
+{category_desc}
+
+只回傳 JSON：
+{json.dumps(json_template, ensure_ascii=False, indent=2)}
+
+物件：{query}"""
+
+
+def get_step2_dynamic_causal_chain_prompt(
+    query: str,
+    categories: List,  # List[CategoryDefinition]
+    attributes_by_category: Dict[str, List[str]],
+    existing_chains: List[Dict[str, str]],
+    chain_index: int
+) -> str:
+    """動態 Step 2 - 生成動態類別的因果鏈"""
+    sorted_cats = sorted(categories, key=lambda x: x.order if hasattr(x, 'order') else x.get('order', 0))
+
+    # 構建可選屬性
+    available_attrs = "\n".join([
+        f"【{cat.name if hasattr(cat, 'name') else cat['name']}】{', '.join(attributes_by_category.get(cat.name if hasattr(cat, 'name') else cat['name'], []))}"
+        for cat in sorted_cats
+    ])
+
+    # 已生成的因果鏈
+    existing_text = ""
+    if existing_chains:
+        chains_list = [
+            " → ".join([chain.get(cat.name if hasattr(cat, 'name') else cat['name'], '?') for cat in sorted_cats])
+            for chain in existing_chains
+        ]
+        existing_text = f"\n【已生成，請勿重複】\n" + "\n".join([f"- {c}" for c in chains_list])
+
+    # JSON 模板
+    json_template = {cat.name if hasattr(cat, 'name') else cat['name']: f"選擇的{cat.name if hasattr(cat, 'name') else cat['name']}" for cat in sorted_cats}
+
+    return f"""/no_think
+為「{query}」生成第 {chain_index} 條因果鏈。
+
+【可選屬性】
+{available_attrs}
+{existing_text}
+
+【規則】
+1. 從每個類別選擇一個屬性
+2. 因果關係必須合理
+3. 不要重複
+
+只回傳 JSON：
+{json.dumps(json_template, ensure_ascii=False, indent=2)}"""