Make fallback coverage something that can actually happen, and say so on the page

fallback.sh starts covered containers with docker start and never creates them, so a coverage list
the partner has never been sent is a promise nothing can keep — all twelve were missing. Adds the
push and remove paths, a readiness card that checks rather than infers, and the fallback state the
assistant needs to answer for it.

Plugin/unraid/Tools/ai_chat_worker.php

@@ -422,6 +422,17 @@ if ($can('system_state')) {
     }
 }
 
+// Fallback is dormant until it isn't, so "configured" and "would work" are unrelated — this is the
+// only block that reports the second. Cheap: local conf and state file plus one cached presence
+// read, never a network round trip.
+if ($can('fallback_state')) {
+    $fb = vv_ai_fallback_state();
+    if ($fb !== '') {
+        $attached['fallback'] = 'readiness';
+        $diagBlock .= $fb;
+    }
+}
+
 // The troubleshooting profile gets the actual tail of the one log the operator is looking at,
 // warnings and ordinary lines alike. The fleet-wide WARN/ERROR sweep above cannot answer "why
 // did this one stop" — the last line a script printed before dying is usually not labelled.