refactor: migrate vendor auth, profile, team, dashboard, settings to modules

Tenancy module (identity & organizational hierarchy):
- vendor_auth.py: login, logout, /me endpoints
- vendor_profile.py: vendor profile get/update
- vendor_team.py: team management, roles, permissions, invitations

Core module (foundational non-domain features):
- vendor_dashboard.py: dashboard statistics
- vendor_settings.py: localization, business info, letzshop settings

All routes auto-discovered via is_self_contained=True.
Deleted 5 legacy files from app/api/v1/vendor/.

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

app/modules/core/definition.py

@@ -15,6 +15,7 @@ core_module = ModuleDefinition(
     description="Dashboard, settings, and profile management. Required for basic operation.",
     version="1.0.0",
     is_core=True,
+    is_self_contained=True,
     features=[
         "dashboard",
         "settings",