feat(fusion_accounting_migration): add Enterprise uninstall safety guard + wizard skeleton

Phase 0 Task 17. Installs a safety guard on ir.module.module that blocks
uninstall of Odoo Enterprise accounting modules (account_accountant,
account_reports, accountant, account_followup, account_asset,
account_budget, account_loans) until the per-module migration flag
fusion_accounting.migration.<name>.completed is set to True. Guard
covers both button_immediate_uninstall (UI) and module_uninstall
(CLI/API) paths, raising UserError with a pointer to the migration
wizard and an escape hatch config parameter.

Also ships a TransientModel fusion.migration.wizard as a shell: it
detects installed Enterprise modules via GUARDED_MODULES and exposes
action_run_migration for sub-modules to extend in later phases. No
per-feature migrations are registered yet -- Phase 1+ sub-modules will
hook in their own steps.

Tests: TestSafetyGuard x2 pass (blocked-when-pending verified with
account_accountant installed; not-blocked-when-completed verified by
setting the flag).

Made-with: Cursor

fusion_accounting_migration/models/ir_module_module.py

@@ -0,0 +1,72 @@
+"""Safety guard: blocks Odoo Enterprise accounting uninstall until migration runs.
+
+For each Enterprise accounting module the user attempts to uninstall, the
+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.
+
+The migration wizard sets the flag to True after a successful migration run
+for that module.
+"""
+
+from odoo import _, api, models
+from odoo.exceptions import UserError
+
+
+GUARDED_MODULES = (
+    'account_accountant',
+    'account_reports',
+    'accountant',
+    'account_followup',
+    'account_asset',
+    'account_budget',
+    'account_loans',
+)
+
+
+class IrModuleModule(models.Model):
+    _inherit = "ir.module.module"
+
+    @api.model
+    def _fusion_check_uninstall_guard(self, module_names):
+        """Verify it's safe to uninstall the given modules.
+
+        Returns True if all checks pass; raises UserError otherwise.
+        """
+        Param = self.env['ir.config_parameter'].sudo()
+        for name in module_names:
+            if name not in GUARDED_MODULES:
+                continue
+            installed = self.sudo().search_count([
+                ('name', '=', name), ('state', '=', 'installed'),
+            ])
+            if not installed:
+                continue
+            flag_key = f'fusion_accounting.migration.{name}.completed'
+            if Param.get_param(flag_key, default='False').lower() != 'true':
+                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"
+                    "and run the migration before uninstalling. Once the "
+                    "migration has completed, the safety guard will allow "
+                    "uninstall.\n\n"
+                    "If you genuinely want to uninstall WITHOUT migrating "
+                    "(data will be lost), set the parameter %s to True manually.",
+                    name, flag_key,
+                ))
+        return True
+
+    def button_immediate_uninstall(self):
+        """Override to invoke the safety guard before allowing uninstall."""
+        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)."""
+        self._fusion_check_uninstall_guard(self.mapped('name'))
+        return super().module_uninstall()