Clarify match full join messaging

src/InvitationPage.jsx

@@ -1969,7 +1969,7 @@ function mapAcceptError(error) {
     return "This invite is no longer available. Ask the host to send a new link.";
   }
   if (status === 409 || code.includes("full")) {
-    return "This match is already full or unavailable.";
+    return "This match is already full or unavailable. Let the organizer know you're available if a spot opens up.";
   }
   if (code.includes("revoked")) {
     return "The host revoked this invite. Ask them for a new link.";

src/TennisMatchApp.jsx

@@ -4331,7 +4331,7 @@ const TennisMatchApp = () => {
                         normalizedMessage.includes("full")
                       ) {
                         displayToast(
-                          "This match is already full. We'll let you know if a spot opens up.",
+                          "This match is already full. Let the organizer know if you're available to sub in.",
                           "error",
                         );
                       } else if (

src/components/MatchDetailsModal.jsx

@@ -1805,7 +1805,8 @@ const MatchDetailsModal = ({
     if (isArchived) return "This match has been archived.";
     if (isCancelled) return "This match has been cancelled.";
     if (!isUpcoming) return "This match is no longer accepting players.";
-    if (isFull) return "This match is currently full.";
+    if (isFull)
+      return "This match is full. Reach out to the organizer if you're available.";
     return null;
   };
 
@@ -1935,7 +1936,7 @@ const MatchDetailsModal = ({
       ) {
         setStatus("full");
         onToast?.(
-          "This match is already full. We'll let you know if a spot opens up.",
+          "This match is already full. Let the organizer know you're available in case a spot opens up.",
           "error",
         );
       } else if (
@@ -2673,7 +2674,7 @@ const MatchDetailsModal = ({
           {status === "full" && !isJoined && (
             <div className="flex items-start gap-3 rounded-2xl border border-amber-200 bg-amber-50 p-4 text-sm font-semibold text-amber-700">
               <AlertCircle className="mt-0.5 h-4 w-4" />
-              This match is currently full. We'll let you know if a spot opens up.
+              This match is currently full. Let the organizer know if you're available to step in.
             </div>
           )}