refactor(fusion_accounting): move AI module code into fusion_accounting_ai sub-module

git mv preserves history. fusion_accounting/ retains only __manifest__.py,
__init__.py, CLAUDE.md, and docs/ — the meta-module shell. All Python,
data, views, security, services, static, tests, wizards, report move to
fusion_accounting_ai/. Manifest data list updated; security.xml move to
_core deferred to Task 12.

Made-with: Cursor

fusion_accounting_ai/controllers/__init__.py

@@ -0,0 +1 @@
+from . import chat_controller