feat(topology): add GHC06 layout and deploy docs

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

topology_api/queries/snapshot_queries.py

@@ -245,8 +245,8 @@ def fetch_snapshot(snapshot_at):
     return result
 
 
-def fetch_layout():
-    """Fetch the default diagram layout with node positions."""
+def fetch_layout(layout_key=None):
+    """Fetch a named diagram layout, falling back to the default layout."""
     with read_cursor() as cur:
         cur.execute("""
             SELECT
@@ -284,9 +284,12 @@ def fetch_layout():
                 ON default_theme.base_id = dl.base_id
                AND default_theme.is_default = true
             WHERE dl.base_id = (SELECT id FROM bases WHERE code = 'guanghan')
-              AND dl.is_default = true
+              AND (
+                  (%(layout_key)s::text IS NOT NULL AND dl.layout_key = %(layout_key)s)
+                  OR (%(layout_key)s::text IS NULL AND dl.is_default = true)
+              )
             ORDER BY dn.z_index, dn.node_key
-        """)
+        """, {"layout_key": layout_key})
         nodes = []
         layout_info = None
         theme_info = None