fix(vision): aggancia i test alla suite di default, skip pulito su 3.11

testpaths include src/vision/tests: prima uv run pytest (365 test) non ci
passava mai. Niente conftest.py: un pytest.importorskip a livello di modulo
in conftest.py rompe l'intera sessione, perche' Skipped eredita da
BaseException e _importconftest cattura solo Exception (verificato con
traceback, provato sia su src/vision/tests sia su src/vision come radice).
La guardia sta invece in cima a test_runner.py, prima di numpy (assente
anch'esso su 3.11) - idioma standard di pytest, cattura pulita a livello di
collection. README aggiornato con il comando reale per farli girare.

src/vision/tests/test_runner.py

@@ -1,7 +1,23 @@
 """Il runner: grafo più immagine, numeri fuori. Niente HTTP, niente database."""
-import numpy as np
 import pytest
 
+# The vision tree requires Python >=3.13 (vs-task/vs-measure/vs-pm2d declare it
+# upstream, see pyproject.toml's `vision` extra), while backend and frontend
+# stay on 3.11. This must run before `import numpy` - numpy itself is only
+# installed alongside the vision extra - so that `uv run pytest` on the
+# default 3.11 environment reports this module as skipped, with a reason,
+# instead of erroring out of the whole collection.
+pytest.importorskip(
+    "visionsuite.task",
+    reason=(
+        "the vision tree requires Python >=3.13 (vs-task/vs-measure/vs-pm2d "
+        "declare it upstream); run it with "
+        "`uv run --python 3.13 --extra vision --extra dev pytest src/vision/tests`"
+    ),
+)
+
+import numpy as np
+
 from src.vision.runner import RunOutcome, engine_version, run_graph