Fix: group membership changes didn't invalidate the User cache

routes/group.js's add/removeMember never called User.clearCache(), unlike
the isServiceAccount handling in routes/user.js (which does this
deliberately, with a comment explaining exactly why). isServiceAccount is
derived at User.get() time from app_sso_service_account membership and
cached for 5 minutes -- so adding or removing a user from ANY group via
this route left group-derived state (isServiceAccount, and by extension
anything else that reads memberOf off a cached User) stale for up to 5
minutes.

In production this manifested as a real user's account appearing to
"vanish": users.ejs's People tab filters out anything with
isServiceAccount truthy, so once that user's membership in
app_sso_service_account changed, they'd disappear from the tab anyone
actually looks at for up to 5 minutes -- looking exactly like data loss,
though the account was never touched. Found by investigating a live "lost
users" report: the account had isServiceAccount: 'yes' and was in fact
still fully present, just hidden.

This does not explain how the account came to be a member of
app_sso_service_account in the first place (unresolved -- possibly a
manual/accidental group-membership change via the Groups UI, which has no
guardrail against adding a real person to what's meant to be a marker
group for non-person accounts). It does fix a real correctness gap: any
admin group-membership change now takes effect immediately instead of on
a timer.

Verified against a real LDAP+Redis harness: the new test fails on the
unfixed code (stale isServiceAccount immediately after the PUT) and
passes with the fix. Full suite: 189/191 passing (2 pre-existing skips).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

nodejs/routes/group.js

@@ -82,8 +82,13 @@ router.put('/:group/:uid', async function(req, res, next){
 
 		var group = await Group.get(req.params.group);
 		var user = await User.get(req.params.uid);
+		const results = await group.addMember(user);
+		// Group membership feeds directly into cached-User-derived state
+		// (isServiceAccount, isAdmin, group-gated nav/UI) -- without this,
+		// a membership change here is invisible for up to the cache's TTL.
+		User.clearCache();
 		return res.json({
-			results: await group.addMember(user),
+			results,
 			message: `Added user ${req.params.uid} to ${req.params.group} group.`
 		});
 	}catch(error){
@@ -98,8 +103,10 @@ router.delete('/:group/:uid', async function(req, res, next){
 
 		var group = await Group.get(req.params.group);
 		var user = await User.get(req.params.uid);
+		const results = await group.removeMember(user);
+		User.clearCache();
 		return res.json({
-			results: await group.removeMember(user),
+			results,
 			message: `Removed user ${req.params.uid} from ${req.params.group} group.`
 		});
 	}catch(error){