清理城市农业类别 + 修复采集器LLM直接选题

清理:
- sustainability_cases.json移除GLO-001/CHN-001城市农业案例,替换为循环消费
- initial_cases.json移除case8东京垂直农场/case26城市屋顶农场
- strategy_topics_to_json.py移除B01/B05/D05三个种菜选题
- collector.py移除城市农业→循环消费映射,更新注释
- 删除fix_collector.py/test_image_gen.py/generate_images.py等遗留脚本
- 删除import_topics.py和automation/下旧版生成脚本

修复:
- collector.py _generate_topic_with_llm不再依赖搜索结果,无搜索时LLM直接生成
- run()始终调用LLM,不再要求web_search_results非空
- 替换sources.yaml中已失效的RSS源(澎湃/虎嗅/中新网→36氪/少数派)

config/sources.yaml

@@ -4,62 +4,33 @@
 sustainability_sources:
   # 中文RSS源（国内媒体，可稳定访问）
   rss:
-    - name: "澎湃新闻-绿政"
+    - name: "36氪-最新"
       type: "rss"
-      url: "https://www.thepaper.cn/rolling_green_news.rss"
+      url: "https://36kr.com/feed"
       update_frequency: "daily"
       credibility: "high"
-      focus: "绿色政策、环境新闻"
-      keywords:
-        - "环保"
-        - "绿色"
-        - "碳"
-        - "生态"
-        - "可持续"
-    - name: "澎湃新闻-最新"
-      type: "rss"
-      url: "https://www.thepaper.cn/rss/rolling.xml"
-      update_frequency: "daily"
-      credibility: "high"
-      focus: "综合新闻"
-      keywords:
-        - "环保"
-        - "绿色"
-        - "碳中和"
-        - "新能源"
-        - "循环"
-        - "可持续"
-        - "低碳"
-        - "垃圾分类"
-    - name: "虎嗅"
-      type: "rss"
-      url: "https://www.huxiu.com/rss/0.xml"
-      update_frequency: "daily"
-      credibility: "medium"
       focus: "科技商业、绿色经济"
       keywords:
-        - "环保"
-        - "绿色"
-        - "碳中和"
+        - "AI"
         - "新能源"
         - "可持续"
+        - "环保"
+        - "绿色"
         - "低碳"
         - "ESG"
         - "循环"
-    - name: "中国新闻网"
+    - name: "少数派"
       type: "rss"
-      url: "https://www.chinanews.com.cn/rss/scroll-news.xml"
+      url: "https://sspai.com/feed"
       update_frequency: "daily"
       credibility: "medium"
-      focus: "综合新闻"
+      focus: "科技数码、效率工具"
       keywords:
-        - "环保"
-        - "绿色"
-        - "碳中和"
-        - "生态"
-        - "新能源"
-        - "垃圾分类"
-        - "低碳"
+        - "AI"
+        - "效率"
+        - "工具"
+        - "数字"
+        - "智能"
 
   # 搜索引擎采集（通过Bing中文搜索抓取热点）
   # 基于《2025中国可持续消费报告》《绿色低碳消费大数据报告》等权威调研得出的七大热点方向