fix(fusion_accounting_migration): add menu + tighten safety-guard test coverage

Addresses code review feedback on Task 17:
- Add menuitem so 'Fusion Accounting -> Migrate from Enterprise' is reachable
  (the UserError guidance now actually works). Placed at top level since
  parenting under fusion_accounting_ai.menu_fusion_accounting_root would
  require adding that module as a hard dep, which is wrong semantically
  (migration should not require AI). Both menuitems carry the admin group
  so the menu stays hidden from users who can't open the wizard anyway.
- Update the UserError wording to "Fusion Accounting -> Migrate from
  Enterprise" (no longer "Settings -> ...") to match the actual menu
  location; 'migration' is preserved per the test's assertIn check.
- Add skipTest guard to test_uninstall_not_blocked_when_migration_completed
  so it doesn't pass vacuously on Community-only CI (the guard's
  `if not installed: continue` would otherwise return True regardless of
  the flag value, giving a false green).
- Move GUARDED_MODULES import to top of wizards/migration_wizard.py
  (no circular-import risk -- models/ir_module_module.py doesn't import
  from wizards/).
- Expand docstrings on button_immediate_uninstall and module_uninstall
  overrides to note they may both fire in a single UI uninstall call
  and that the guard is idempotent (pure read + raise).

Made-with: Cursor

fusion_accounting_migration/models/ir_module_module.py

@@ -6,8 +6,8 @@ guard checks an ir.config_parameter flag named:
     fusion_accounting.migration.<module_name>.completed
 
 If the flag is False/unset and the module is currently installed, the guard
-raises UserError pointing the user to Settings -> Fusion Accounting ->
-Migrate from Enterprise.
+raises UserError pointing the user to the top-level
+Fusion Accounting -> Migrate from Enterprise menu.
 
 The migration wizard sets the flag to True after a successful migration run
 for that module.
@@ -51,7 +51,7 @@ class IrModuleModule(models.Model):
                 raise UserError(_(
                     "Cannot uninstall %s: the Fusion Accounting migration "
                     "for this module has not run yet. Please open\n"
-                    "    Settings -> Fusion Accounting -> Migrate from Enterprise\n"
+                    "    Fusion Accounting -> Migrate from Enterprise\n"
                     "and run the migration before uninstalling. Once the "
                     "migration has completed, the safety guard will allow "
                     "uninstall.\n\n"
@@ -62,11 +62,23 @@ class IrModuleModule(models.Model):
         return True
 
     def button_immediate_uninstall(self):
-        """Override to invoke the safety guard before allowing uninstall."""
+        """Override to invoke the safety guard before allowing uninstall.
+
+        Both this and ``module_uninstall`` below can fire in a single UI
+        uninstall call (button_immediate_uninstall -> module_uninstall). The
+        guard is a pure read + raise, so re-running it is idempotent: on the
+        happy path it just re-confirms; on the blocked path the first call
+        already raised and the second is never reached.
+        """
         self._fusion_check_uninstall_guard(self.mapped('name'))
         return super().button_immediate_uninstall()
 
     def module_uninstall(self):
-        """Override the lower-level uninstall path too (CLI / API uninstall)."""
+        """Override the lower-level uninstall path too (CLI / API uninstall).
+
+        See ``button_immediate_uninstall`` above -- both overrides may run in
+        the same UI uninstall; the guard is idempotent so double-invocation
+        is safe.
+        """
         self._fusion_check_uninstall_guard(self.mapped('name'))
         return super().module_uninstall()