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/exceptions.py

@@ -0,0 +1,38 @@
+# app/modules/tenancy/exceptions.py
+"""
+Tenancy module exceptions.
+
+Exceptions for platform, company, vendor, and admin user management.
+"""
+
+from app.exceptions import WizamartException
+
+
+class TenancyException(WizamartException):
+    """Base exception for tenancy module."""
+
+    pass
+
+
+class VendorNotFoundException(TenancyException):
+    """Vendor not found or inactive."""
+
+    def __init__(self, vendor_code: str):
+        super().__init__(f"Vendor '{vendor_code}' not found or inactive")
+        self.vendor_code = vendor_code
+
+
+class CompanyNotFoundException(TenancyException):
+    """Company not found."""
+
+    def __init__(self, company_id: int):
+        super().__init__(f"Company {company_id} not found")
+        self.company_id = company_id
+
+
+class PlatformNotFoundException(TenancyException):
+    """Platform not found."""
+
+    def __init__(self, platform_id: int):
+        super().__init__(f"Platform {platform_id} not found")
+        self.platform_id = platform_id