fix(423): handle RateLimitHardBlock in ws.rs match

The new WatcherEvent::RateLimitHardBlock variant added in the feature
commit was not covered in the ws.rs From<WatcherEvent> match, causing
a compile error. Add the missing arm returning None (same as
RateLimitWarning — handled by chat notifications only, not WebSocket).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/src/http/ws.rs

@@ -163,6 +163,7 @@ impl From<WatcherEvent> for Option<WsResponse> {
             WatcherEvent::MergeFailure { .. } => None,
             WatcherEvent::RateLimitWarning { .. } => None,
             WatcherEvent::StoryBlocked { .. } => None,
+            WatcherEvent::RateLimitHardBlock { .. } => None,
         }
     }
 }