fix: add interrupt_on_new_message support for Matrix channel (#4070)

Add the missing interrupt_on_new_message field to MatrixConfig and wire
it through InterruptOnNewMessageConfig so Matrix behaves consistently
with Telegram, Slack, Discord, and Mattermost.

Closes #4058

src/integrations/registry.rs

@@ -890,6 +890,7 @@ mod tests {
             device_id: None,
             room_id: "!r:m".into(),
             allowed_users: vec![],
+            interrupt_on_new_message: false,
         });
         let entries = all_integrations();
         let mx = entries.iter().find(|e| e.name == "Matrix").unwrap();