refactor: migrate vendor billing, invoices, payments to module auto-discovery

Billing module:
- Create vendor_checkout.py (checkout, portal, cancel, reactivate, change-tier)
- Create vendor_addons.py (addon management routes)
- Update vendor.py to aggregate new routers

Orders module:
- Create vendor_invoices.py (invoice settings, CRUD, PDF generation)
- Update vendor.py to aggregate invoices router

Payments module:
- Restructure routes from routes/ to routes/api/
- Add require_module_access dependency
- Set is_self_contained=True for auto-discovery

Remove legacy files:
- app/api/v1/vendor/billing.py
- app/api/v1/vendor/invoices.py
- app/api/v1/vendor/payments.py

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

app/modules/billing/routes/api/vendor_checkout.py

@@ -0,0 +1,220 @@
+# app/modules/billing/routes/api/vendor_checkout.py
+"""
+Vendor checkout and subscription management endpoints.
+
+Provides:
+- Stripe checkout session creation
+- Stripe portal session creation
+- Subscription cancellation and reactivation
+- Upcoming invoice preview
+- Tier changes (upgrade/downgrade)
+
+All routes require module access control for the 'billing' module.
+"""
+
+import logging
+
+from fastapi import APIRouter, Depends
+from pydantic import BaseModel
+from sqlalchemy.orm import Session
+
+from app.api.deps import get_current_vendor_api, require_module_access
+from app.core.config import settings
+from app.core.database import get_db
+from app.modules.billing.services import billing_service, subscription_service
+from models.schema.auth import UserContext
+
+vendor_checkout_router = APIRouter(
+    dependencies=[Depends(require_module_access("billing"))],
+)
+logger = logging.getLogger(__name__)
+
+
+# ============================================================================
+# Schemas
+# ============================================================================
+
+
+class CheckoutRequest(BaseModel):
+    """Request to create a checkout session."""
+
+    tier_code: str
+    is_annual: bool = False
+
+
+class CheckoutResponse(BaseModel):
+    """Checkout session response."""
+
+    checkout_url: str
+    session_id: str
+
+
+class PortalResponse(BaseModel):
+    """Customer portal session response."""
+
+    portal_url: str
+
+
+class CancelRequest(BaseModel):
+    """Request to cancel subscription."""
+
+    reason: str | None = None
+    immediately: bool = False
+
+
+class CancelResponse(BaseModel):
+    """Cancellation response."""
+
+    message: str
+    effective_date: str
+
+
+class UpcomingInvoiceResponse(BaseModel):
+    """Upcoming invoice preview."""
+
+    amount_due_cents: int
+    currency: str
+    next_payment_date: str | None = None
+    line_items: list[dict] = []
+
+
+class ChangeTierRequest(BaseModel):
+    """Request to change subscription tier."""
+
+    tier_code: str
+    is_annual: bool = False
+
+
+class ChangeTierResponse(BaseModel):
+    """Response for tier change."""
+
+    message: str
+    new_tier: str
+    effective_immediately: bool
+
+
+# ============================================================================
+# Endpoints
+# ============================================================================
+
+
+@vendor_checkout_router.post("/checkout", response_model=CheckoutResponse)
+def create_checkout_session(
+    request: CheckoutRequest,
+    current_user: UserContext = Depends(get_current_vendor_api),
+    db: Session = Depends(get_db),
+):
+    """Create a Stripe checkout session for subscription."""
+    vendor_id = current_user.token_vendor_id
+    vendor = billing_service.get_vendor(db, vendor_id)
+
+    # Build URLs
+    base_url = f"https://{settings.platform_domain}"
+    success_url = f"{base_url}/vendor/{vendor.vendor_code}/billing?success=true"
+    cancel_url = f"{base_url}/vendor/{vendor.vendor_code}/billing?cancelled=true"
+
+    result = billing_service.create_checkout_session(
+        db=db,
+        vendor_id=vendor_id,
+        tier_code=request.tier_code,
+        is_annual=request.is_annual,
+        success_url=success_url,
+        cancel_url=cancel_url,
+    )
+    db.commit()
+
+    return CheckoutResponse(checkout_url=result["checkout_url"], session_id=result["session_id"])
+
+
+@vendor_checkout_router.post("/portal", response_model=PortalResponse)
+def create_portal_session(
+    current_user: UserContext = Depends(get_current_vendor_api),
+    db: Session = Depends(get_db),
+):
+    """Create a Stripe customer portal session."""
+    vendor_id = current_user.token_vendor_id
+    vendor = billing_service.get_vendor(db, vendor_id)
+    return_url = f"https://{settings.platform_domain}/vendor/{vendor.vendor_code}/billing"
+
+    result = billing_service.create_portal_session(db, vendor_id, return_url)
+
+    return PortalResponse(portal_url=result["portal_url"])
+
+
+@vendor_checkout_router.post("/cancel", response_model=CancelResponse)
+def cancel_subscription(
+    request: CancelRequest,
+    current_user: UserContext = Depends(get_current_vendor_api),
+    db: Session = Depends(get_db),
+):
+    """Cancel subscription."""
+    vendor_id = current_user.token_vendor_id
+
+    result = billing_service.cancel_subscription(
+        db=db,
+        vendor_id=vendor_id,
+        reason=request.reason,
+        immediately=request.immediately,
+    )
+    db.commit()
+
+    return CancelResponse(
+        message=result["message"],
+        effective_date=result["effective_date"],
+    )
+
+
+@vendor_checkout_router.post("/reactivate")
+def reactivate_subscription(
+    current_user: UserContext = Depends(get_current_vendor_api),
+    db: Session = Depends(get_db),
+):
+    """Reactivate a cancelled subscription."""
+    vendor_id = current_user.token_vendor_id
+
+    result = billing_service.reactivate_subscription(db, vendor_id)
+    db.commit()
+
+    return result
+
+
+@vendor_checkout_router.get("/upcoming-invoice", response_model=UpcomingInvoiceResponse)
+def get_upcoming_invoice(
+    current_user: UserContext = Depends(get_current_vendor_api),
+    db: Session = Depends(get_db),
+):
+    """Preview the upcoming invoice."""
+    vendor_id = current_user.token_vendor_id
+
+    result = billing_service.get_upcoming_invoice(db, vendor_id)
+
+    return UpcomingInvoiceResponse(
+        amount_due_cents=result.get("amount_due_cents", 0),
+        currency=result.get("currency", "EUR"),
+        next_payment_date=result.get("next_payment_date"),
+        line_items=result.get("line_items", []),
+    )
+
+
+@vendor_checkout_router.post("/change-tier", response_model=ChangeTierResponse)
+def change_tier(
+    request: ChangeTierRequest,
+    current_user: UserContext = Depends(get_current_vendor_api),
+    db: Session = Depends(get_db),
+):
+    """Change subscription tier (upgrade/downgrade)."""
+    vendor_id = current_user.token_vendor_id
+
+    result = billing_service.change_tier(
+        db=db,
+        vendor_id=vendor_id,
+        new_tier_code=request.tier_code,
+        is_annual=request.is_annual,
+    )
+    db.commit()
+
+    return ChangeTierResponse(
+        message=result["message"],
+        new_tier=result["new_tier"],
+        effective_immediately=result["effective_immediately"],
+    )