feat: 新增360/搜狗/微信搜索提供商 + PG15→16升级 & 项目文档更新

- search_utils.py: 新增 _call_360/_call_sogou/_call_wechat HTML爬取函数
- initial_data.py: 种子数据新增三个搜索提供商（priority 3/4/5）
- models.py: provider_type 注释补充新类型
- admin.html: 搜索提供商类型下拉框新增三个选项
- AGENTS.md/PROGRESS.md/README.md: PostgreSQL 15→16
- README.md: 移除硬编码数据库密码

platform/backend/app/initial_data.py

@@ -76,6 +76,9 @@ def import_initial_data():
             providers = [
                 SearchProvider(name="百度千帆", provider_type="baidu", api_key="", api_url="https://qianfan.baidubce.com/v2/ai_search/web_search", console_url="https://console.bce.baidu.com/qianfan/ais/console/onlineService", priority=1, enabled=True, daily_limit=50),
                 SearchProvider(name="opencode云搜索", provider_type="mcp", api_key="", api_url="", console_url="https://opencode.ai", priority=2, enabled=True, daily_limit=99999),
+                SearchProvider(name="360搜索", provider_type="360", api_key="", api_url="", console_url="https://www.so.com", priority=3, enabled=True, daily_limit=200),
+                SearchProvider(name="搜狗搜索", provider_type="sogou", api_key="", api_url="", console_url="https://sogou.com", priority=4, enabled=True, daily_limit=200),
+                SearchProvider(name="微信搜一搜", provider_type="wechat", api_key="", api_url="", console_url="https://wx.sogou.com/weixin", priority=5, enabled=True, daily_limit=200),
             ]
             for p in providers:
                 db.add(p)