fix(alerts): Better messaging for missing snoozeCreatedBy (#112506)

Fixes ISWF-2409.

Before:
<img width="860" height="197" alt="Screenshot 2026-04-08 at 12 34 30 PM"
src="https://github.com/user-attachments/assets/2740589d-7c49-4f35-81a9-276c6896e407"
/>


After:
<img width="679" height="207" alt="Screenshot 2026-04-08 at 12 34 06 PM"
src="https://github.com/user-attachments/assets/c1efa3f1-cee8-4e2a-86f6-cdce5b11eec4"
/>

Author: kcons

static/app/views/alerts/rules/issue/details/ruleDetails.tsx

@@ -473,12 +473,14 @@ export default function AlertRuleDetails() {
               <Alert.Container>
                 {rule.snoozeForEveryone ? (
                   <Alert variant="info">
-                    {tct(
-                      "[creator] muted this alert for everyone so you won't get these notifications in the future.",
-                      {
-                        creator: rule.snoozeCreatedBy,
-                      }
-                    )}
+                    {rule.snoozeCreatedBy
+                      ? tct(
+                          "[creator] muted this alert for everyone so you won't get these notifications in the future.",
+                          {creator: rule.snoozeCreatedBy}
+                        )
+                      : t(
+                          "This alert has been muted for everyone so you won't get these notifications in the future."
+                        )}
                   </Alert>
                 ) : (
                   <UserSnoozeDeprecationBanner projectId={project.id} />

static/app/views/alerts/rules/metric/details/body.tsx

@@ -175,12 +175,14 @@ export function MetricDetailsBody({
             <Alert.Container>
               {rule.snoozeForEveryone ? (
                 <Alert variant="info">
-                  {tct(
-                    "[creator] muted this alert for everyone so you won't get these notifications in the future.",
-                    {
-                      creator: rule.snoozeCreatedBy,
-                    }
-                  )}
+                  {rule.snoozeCreatedBy
+                    ? tct(
+                        "[creator] muted this alert for everyone so you won't get these notifications in the future.",
+                        {creator: rule.snoozeCreatedBy}
+                      )
+                    : t(
+                        "This alert has been muted for everyone so you won't get these notifications in the future."
+                      )}
                 </Alert>
               ) : (
                 <UserSnoozeDeprecationBanner projectId={project.id} />