issues/27: fix mermaid git-flow diagram

infrastructure/test-contour/git-flow.md

@@ -25,20 +25,16 @@
 **Правило:** feature-ветки **всегда** ответвляются от `prod`, не от `test` и не от `stage`.
 
 ```mermaid
-gitGraph
-  commit id: "prod baseline"
-  branch test
-  branch stage
-  checkout prod
-  branch feature/TASK-123
-  commit id: "implement"
-  checkout test
-  merge feature/TASK-123 id: "PR → test"
-  checkout feature/TASK-123
-  checkout stage
-  merge feature/TASK-123 id: "PR → stage (NOT test!)"
-  checkout prod
-  merge stage id: "release: stage → prod"
+flowchart TB
+  prod([prod])
+  test([test])
+  stage([stage])
+  feat[feature/TASK-123]
+
+  prod -->|ветка от prod| feat
+  feat -->|PR merge| test
+  feat -->|PR merge — не test| stage
+  stage -->|release PR| prod
 ```
 
 ### ⚠️ Частая ошибка