fix(dashboard): cache org stats in Redis with versioned invalidation (#883)

* fix(dashboard): cache org stats in Redis with versioned invalidation

Replace the never-expiring process-local cache in the org dashboard page
load with API-side Redis caching keyed per org. A version stamp prevents
slow reads from writing pre-purge data back into the cache.

Invalidate on course create/update/delete, student enroll/remove, certificate
claim, and progress reset. Remove the dashboard SSR module cache so every
page load reads through the API cache layer.

Fixes #852

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(dashboard): address PR review on stats cache invalidation

- Validate bust via ZDashStats instead of raw query access
- Use import type for OrganisationAnalytics
- Resolve orgId before course delete so invalidation is reliable
- Invalidate immediately after persisted writes, before fallible side effects
- Invalidate on member role changes and program course access enrollment

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(dashboard): complete stats cache invalidation coverage

Wire org stats cache purge on lesson completion (manual toggle and
video-watch auto-complete) so topCourses completion percentages stay
fresh. Harden bulk member adds with sequential inserts and a finally
invalidation boundary, and only purge org invite enrollments when new
group memberships were actually inserted.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(core): make lesson completion stats purge best-effort

Wrap org stats cache invalidation in try/catch so a lookup or Redis
failure cannot turn a successful lesson completion into a 500.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(dashboard): keep org stats cache through lesson completion

Lesson complete is a high-frequency event and usually does not change
the rounded dashboard percentages. Rely on a 10 minute TTL instead of
purging the snapshot on every completion.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* docs: explain how admin dashboard numbers are calculated

Add a user-facing guide covering headline counts, top courses,
certificates, login activity, and when the 10 minute snapshot refreshes.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

---------

apps/dashboard/src/routes/(app)/org/[slug]/dash/+page.server.ts

@@ -2,9 +2,6 @@ import type { DashStatsSuccess, LoginActivityData, LoginActivitySuccess } from '
 import { classroomio, getApiHeaders } from '$lib/utils/services/api';
 import { type ServerApiResult, safeServerApi } from '$lib/utils/services/api/server';
 
-// TODO - Replace with actual cache
-const cache: Record<string, DashStatsSuccess['data'] | null> = {};
-
 function loginActivityDataFromSettled(
   result: PromiseSettledResult<ServerApiResult<LoginActivitySuccess>>
 ): LoginActivityData {
@@ -26,18 +23,6 @@ export const load = async ({ params, parent, cookies }) => {
     };
   }
 
-  if (orgId in cache) {
-    const loginActivityResult = await safeServerApi<LoginActivitySuccess>(() =>
-      classroomio.dash['login-activity'].$get({ query: { orgId } }, getApiHeaders(cookies, orgId))
-    );
-
-    return {
-      orgName: siteName,
-      stats: cache[orgId],
-      loginActivity: loginActivityResult.ok ? loginActivityResult.body.data : []
-    };
-  }
-
   const [statsResult, loginActivityResult] = await Promise.allSettled([
     safeServerApi<DashStatsSuccess>(() =>
       classroomio.dash.stats.$get({ query: { siteName } }, getApiHeaders(cookies, orgId))
@@ -47,11 +32,11 @@ export const load = async ({ params, parent, cookies }) => {
     )
   ]);
 
-  cache[orgId] = statsResult.status === 'fulfilled' && statsResult.value.ok ? statsResult.value.body.data : null;
+  const stats = statsResult.status === 'fulfilled' && statsResult.value.ok ? statsResult.value.body.data : null;
 
   return {
     orgName: siteName,
-    stats: cache[orgId],
+    stats,
     loginActivity: loginActivityDataFromSettled(loginActivityResult)
   };
 };