ci: migrate tests to reusable workflows and introduce stable-tag pipeline

- convert all test workflows to reusable workflow_call
- add central CI workflow for branches and PRs
- add mark-stable workflow triggered on main pushes
- ensure stable tag updates only after all tests succeed
- remove duplicated triggers from test workflows
`

https://chatgpt.com/share/693aa4a6-7460-800f-ba47-cfc15b1b2236

.github/workflows/test-virgin-root.yml

@@ -1,13 +1,7 @@
 name: Test Virgin Root
 
 on:
-  push:
-    branches:
-      - main
-      - master
-      - develop
-      - "*"
-  pull_request:
+  workflow_call:
 
 jobs:
   test-virgin-root: