fix: 三平台内容差异化 + admin敏感词管理表格化

- writer.py: _expand_section() 去除 <100字阈值，始终调用 LLM 平台专属扩写
- prompt_loader.py: 新增 section_expansion_zhihu/wechat/xiaohongshu 三个独立 prompt
- admin.html: 配置管理标签页 + 敏感词/清理规则子标签 + 敏感词表格化管理(编辑/删除)
- config_items.py: PUT /sensitive-words/{id} 支持更新 word/category
- compliance_checker.py: AI 套话从 DB 加载 + 人称规则修正
- initial_data.py: PlatformConfig 字数迁移 + 新种子
- 各前端页面: LLM 配置 rate_limit 字段 + 供应商列表排序

platform/backend/app/database.py

@@ -48,12 +48,15 @@ def init_db():
             conn.execute(text("ALTER TABLE llm_configs ADD COLUMN IF NOT EXISTS base_url VARCHAR"))
             conn.execute(text("ALTER TABLE llm_configs ADD COLUMN IF NOT EXISTS api_key VARCHAR"))
             conn.execute(text("ALTER TABLE llm_configs ADD COLUMN IF NOT EXISTS is_default BOOLEAN DEFAULT FALSE"))
+            conn.execute(text("ALTER TABLE llm_configs ADD COLUMN IF NOT EXISTS rate_limit INTEGER DEFAULT 0"))
+            conn.execute(text("ALTER TABLE llm_configs ADD COLUMN IF NOT EXISTS rate_limit_window_minutes INTEGER DEFAULT 300"))
             try:
                 conn.execute(text("ALTER TABLE articles ADD COLUMN IF NOT EXISTS images JSON DEFAULT '{}'::json"))
             except Exception:
                 conn.execute(text("ALTER TABLE articles ADD COLUMN IF NOT EXISTS images TEXT DEFAULT '{}'"))
             for table, col, typ in [
                 ("users", "org_id", "VARCHAR DEFAULT 'default'"),
+                ("articles", "updated_at", "TIMESTAMP"),
                 ("topics", "org_id", "VARCHAR DEFAULT 'default'"),
                 ("topics", "reviewed_at", "TIMESTAMP"),
                 ("platform_configs", "requires_image", "BOOLEAN DEFAULT FALSE"),