feat(analytics): retire Rybbit and add SEO/GEO discovery tracking

Document Umami as the sole analytics platform, remove Rybbit proxy and
tracker code, and classify public page traffic with discovery_channel for
adm SEO/GEO dashboards.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/branch-disposition.md

@@ -17,6 +17,8 @@
 
 **状态：禁止再次引用。改动已提交并进入 `origin/main`，该分支保留仅用于只读追溯，不是待合并开发分支。**
 
+> **2026-08 补充**：该分支引入的 Rybbit tracking 已于 2026-08 全量下线并自代码库移除；当前访问统计 **仅 Umami**，见 [analytics-platform.md](analytics-platform.md)。勿再从本分支恢复 Rybbit 相关实现。
+
 审计日期：2026-07-27
 分支 HEAD：`90ee4c3`
 `origin/main` 对应提交：`90ee4c3`
@@ -40,7 +42,7 @@
 
 本分支闭环前已通过：
 
-- `node --test mindspace-rybbit.test.mjs server/portal-domain-services-bootstrap.test.mjs server/portal-published-page-delivery.test.mjs server/portal-publication-shell.test.mjs`
+- `node --test mindspace-analytics.test.mjs mindspace-analytics-discovery.test.mjs server/portal-domain-services-bootstrap.test.mjs server/portal-published-page-delivery.test.mjs server/portal-publication-shell.test.mjs`（历史验证含 `mindspace-rybbit.test.mjs`，Rybbit 已移除）
 - `npm run verify:chat-finish-sync`
 - `npm run verify:mindspace-publish-guards`
 - `npm run verify:mindspace-publish-guards:full`