feat(server): gate scheduling, search and login by site capabilities (IA-2)

- snapshots only for sites with list; feed polling only for RSS kinds;
  user data / health checks only for sites with login; search site set
  only includes searchable sites; live search / snapshot skip with
  reason unsupported instead of hitting the site
- refresh-login / credentials need login, manual snapshot needs list (400)
- POST /sites accepts kind and rssUrl (site + feed in one transaction,
  key generated from host); RSS belongs to a site: feeds created without
  siteId go to the same-host custom RSS source site, siteId cannot be
  cleared
- fix: secret name clash when a site gets a second default-named feed
- command palette regrouped; agent site.list returns kind and
  capabilities; system prompt notes RSS lives under sites

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/agent/src/system-prompt.ts

@@ -84,6 +84,7 @@ export function buildSystemPrompt({
     '检索词要有意义:写作品名、别名或关键词;不要用空串、单个字母或通配符(如 query:"a"、"*")探查全表,想盘点就用对应的列表能力(inventory.query 不带 query、subscription.list、decision.list)。',
     '参数按工具 schema 的类型填写:ID 类参数一律是字符串(如 externalId:"693134",不是数字 693134);不要传 schema 里没有的字段。',
     "业务任务 ID 用 task.inspect,下载任务 ID 或种子 hash 用 download.inspect,两者不要混用。",
+    "站点分类型:PT 站、公开 BT 站、自定义 RSS 源;RSS 属于站点(在站点详情的 RSS 里管理),没有单独的 RSS 页。能不能搜索、抓列表、登录看 site.list 返回的获取方式,不支持的不要去试。",
     "思考、步骤说明和汇报都用中文;引用文件名、原站标题时保持原文。",
     "工具结果里出现【预算提醒】时立刻停止探查,直接用中文写小结;被预算或中止打断时,汇报只写中文小结(已完成什么、证据、还缺什么),不要复述中间过程或下一步打算。",
   ];