docs: ignore box diagrams in ascii guard

Wrap existing box-drawing diagrams with ascii-guard markers so docs-site checks pass when website docs are touched.

Co-authored-by: Cursor <cursoragent@cursor.com>

website/docs/user-guide/features/kanban.md

@@ -494,6 +494,7 @@ And the two auxiliary LLM slots:
 
 The GUI is strictly a **read-through-the-DB + write-through-kanban_db** layer with no domain logic of its own:
 
+<!-- ascii-guard-ignore -->
 ```
 ┌────────────────────────┐      WebSocket (tails task_events)
 │   React SPA (plugin)   │ ◀──────────────────────────────────┐
@@ -513,6 +514,7 @@ The GUI is strictly a **read-through-the-DB + write-through-kanban_db** layer wi
 │  (WAL, shared)         │
 └────────────────────────┘
 ```
+<!-- ascii-guard-ignore-end -->
 
 ### REST surface