refactor: move vendor info endpoint to tenancy module

MIGRATION:
- Move app/api/v1/vendor/info.py to app/modules/tenancy/routes/api/vendor.py
- Change endpoint path from GET /{vendor_code} to GET /info/{vendor_code}
- Remove catch-all route ordering dependency

TENANCY MODULE SETUP:
- Mark tenancy module as is_self_contained=True
- Add routes/api/vendor.py with vendor_router
- Add exceptions.py with TenancyException hierarchy
- Add placeholder __init__.py files for services, models, schemas

FRONTEND UPDATES:
- Update static/vendor/js/login.js to use new /vendor/info/{vendor_code} path
- Update static/vendor/js/init-alpine.js to use new /vendor/info/{vendor_code} path

The new path is more explicit and eliminates the need for catch-all route
ordering in the vendor router aggregation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/modules/tenancy/definition.py

@@ -15,6 +15,7 @@ tenancy_module = ModuleDefinition(
     description="Platform, company, vendor, and admin user management. Required for multi-tenant operation.",
     version="1.0.0",
     is_core=True,
+    is_self_contained=True,
     features=[
         "platform_management",
         "company_management",
@@ -32,6 +33,10 @@ tenancy_module = ModuleDefinition(
             "team",
         ],
     },
+    services_path="app.modules.tenancy.services",
+    models_path="app.modules.tenancy.models",
+    schemas_path="app.modules.tenancy.schemas",
+    exceptions_path="app.modules.tenancy.exceptions",
 )
 
 __all__ = ["tenancy_module"]