Don't block type changes on a pre-existing répartition écart

updateType() only ever touches field_type_ligne (and possibly
field_entree_liee) -- never montant_ht or field_repartition -- so it
can't introduce a new répartition mismatch, only leave an existing
one (preserved from historical data, per the module's own docblock)
untouched. Wrap the save in the same skip_validation state flag the
migration scripts use, scoped tightly with try/finally so it always
clears even if save() throws for an unrelated reason.

Verified: changing the type of a line with a known -0.02€ écart now
succeeds, the écart is unchanged afterward (montant_ht and the
répartition sum both identical to before), and the state flag reads
back unset once the request completes.

web/modules/custom/figli_compta_ledger/src/Controller/LedgerActionsController.php

@@ -66,12 +66,26 @@ class LedgerActionsController extends ControllerBase {
       $node->set('field_entree_liee', NULL);
     }
 
+    // Only field_type_ligne (and possibly field_entree_liee) changes here
+    // -- montant_ht and field_repartition are untouched, so this can never
+    // *introduce* a répartition mismatch, only leave a pre-existing one
+    // (from historical data, never corrected -- see figli_compta_ledger's
+    // module docblock) exactly as it was. The présave check exists to
+    // catch new inconsistent entries, not to block relabeling the type of
+    // an already-migrated line, so skip it for this save only. try/finally
+    // guarantees the global flag clears even if save() throws for an
+    // unrelated reason -- leaving it on would silently skip validation on
+    // every other save on the site.
+    \Drupal::state()->set('figli_compta_ledger.skip_validation', TRUE);
     try {
       $node->save();
     }
     catch (EntityStorageException $e) {
       return new JsonResponse(['error' => $e->getMessage()], 422);
     }
+    finally {
+      \Drupal::state()->delete('figli_compta_ledger.skip_validation');
+    }
 
     return new JsonResponse([
       'success' => TRUE,