feat(health): wire H5 health page, WeChat channel, and observation API.

Expose /health and /api/health/observations behind MEMIND_HEALTH_ENABLED, redirect ordinary chat health intents without persisting, and run a dedicated WeChat menu flow with confirm-before-write semantics.

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

src/types.ts

@@ -1016,6 +1016,7 @@ export type AuthStatus = {
   unrestricted?: boolean;
   agentCodeRun?: AgentCodeRunClientPolicy | null;
   goalRun?: GoalRunClientPolicy | null;
+  health?: { enabled: boolean } | null;
 };
 
 export type PageTemplateCatalogItem = {