minor: renumber mermaid diagrams (#36)

Author: liady

specification/draft/apps.mdx

@@ -743,7 +743,7 @@ sequenceDiagram
 
 Note: when the Guest UI is rendered inside a sandbox, the sandbox transparently passes messages between the Guest UI and the Host, except for messages named `ui/notifications/sandbox-*`.
 
-#### 5. Interactive Phase
+#### 3. Interactive Phase
 
 ```mermaid
 sequenceDiagram
@@ -782,7 +782,7 @@ sequenceDiagram
   end
 ```
 
-#### 6. Cleanup
+#### 4. Cleanup
 
 ```mermaid
 sequenceDiagram