Block server destruction while linked to an active beta

Protect individual, bulk, and queued removals and rebuilds until beta closure. Recheck ownership before teardown and reject beta admission during pending or unresolved destruction.

Fixes #36

README.md

@@ -172,6 +172,8 @@ or unreachable servers remain queued. Containers, server files, and registration
 are removed, while saved keys and collections are retained. The preview must be
 reviewed again if fleet membership changes before confirmation. Servers created
 after confirmation are not included. Progress appears in deployment history.
+If any target belongs to an active beta, no removals are queued. Promote or roll
+back that beta before retrying fleet removal or an exact collection launch.
 
 If deletion fails after Komodo removal, the operation detail page offers
 **Resume cleanup** to retry local file and database removal without RCON or
@@ -405,8 +407,10 @@ Deleting a server preserves its name, recorded beta progress and test evidence,
 campaign results and file diffs, provisioning and maintenance history, and match
 records. Historical entries show **Deleted** and omit live server links and
 actions. Reusing the same server name starts a new instance; old records remain
-marked deleted, and old work cannot target the replacement. Deleting a participant
-pauses an open beta; roll it back and open a new beta to test the replacement.
+marked deleted, and old work cannot target the replacement. Servers linked to an
+active beta cannot be destroyed or rebuilt until that beta is promoted or rolled
+back. A participant removed outside provisioning still pauses its open beta; roll
+it back and open a new beta to test the replacement.
 Normal history retention still applies. Records erased by earlier versions cannot
 be restored by this upgrade. Existing history is marked deleted where the server
 is already absent; instances that reused a name before upgrading cannot always be