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>

release-gate/coverage.mjs

@@ -942,7 +942,7 @@ export const AUTOMATION_SUITES = Object.freeze([
       'services/orchestrator/shadow-observer.test.mjs',
       'services/orchestrator/observability.test.mjs',
       'mindspace-analytics.test.mjs',
-      'mindspace-rybbit.test.mjs',
+      'mindspace-analytics-discovery.test.mjs',
       'system-disclosure-policy.test.mjs',
     ],
   },

release-gate/local-stack.mjs

@@ -547,7 +547,6 @@ export async function createLocalGateStack({
       H5_REMINDER_WORKER_ENABLED: '0',
       MEMIND_ANALYTICS_ENABLED: '0',
       MINDSPACE_ANALYTICS_ENABLED: '0',
-      MEMIND_RYBBIT_ENABLED: 'false',
     };
     baseUrl = `http://127.0.0.1:${port}`;
     if (beforePortalStart) {

release-gate/public-url.mjs

@@ -8,7 +8,6 @@ const ALLOWED_TKMIND_HOSTS = new Set([
   'go.tkmind.cn',
   'm.tkmind.cn',
   'plaza.tkmind.cn',
-  'rybbit.tkmind.cn',
 ]);
 
 function isPrivateIpv4(hostname) {