feat: add invoicing system and subscription tier enforcement

Phase 1 OMS implementation:

Invoicing:
- Add Invoice and VendorInvoiceSettings database models
- Full EU VAT support (27 countries, OSS, B2B reverse charge)
- Invoice PDF generation with WeasyPrint + Jinja2 templates
- Vendor invoice API endpoints for settings, creation, PDF download

Subscription Tiers:
- Add VendorSubscription model with 4 tiers (Essential/Professional/Business/Enterprise)
- Tier limit enforcement for orders, products, team members
- Feature gating based on subscription tier
- Automatic trial subscription creation for new vendors
- Integrate limit checks into order creation (direct and Letzshop sync)

Marketing:
- Update pricing documentation with 4-tier structure
- Revise back-office positioning strategy
- Update homepage with Veeqo-inspired Letzshop-focused messaging

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

alembic/versions/i7d8e9f0a1b2_add_vendor_subscriptions.py

@@ -0,0 +1,148 @@
+"""Add vendor subscriptions table
+
+Revision ID: i7d8e9f0a1b2
+Revises: h6c7d8e9f0a1
+Create Date: 2025-12-24
+
+This migration adds:
+- vendor_subscriptions: Per-vendor subscription tracking with tier limits
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "i7d8e9f0a1b2"
+down_revision: Union[str, None] = "h6c7d8e9f0a1"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # Create vendor_subscriptions table
+    op.create_table(
+        "vendor_subscriptions",
+        sa.Column("id", sa.Integer(), nullable=False),
+        sa.Column("vendor_id", sa.Integer(), nullable=False),
+        # Tier and status
+        sa.Column(
+            "tier", sa.String(length=20), server_default="essential", nullable=False
+        ),
+        sa.Column(
+            "status", sa.String(length=20), server_default="trial", nullable=False
+        ),
+        # Billing period
+        sa.Column("period_start", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("period_end", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("is_annual", sa.Boolean(), server_default="0", nullable=False),
+        # Trial
+        sa.Column("trial_ends_at", sa.DateTime(timezone=True), nullable=True),
+        # Usage counters
+        sa.Column("orders_this_period", sa.Integer(), server_default="0", nullable=False),
+        sa.Column("orders_limit_reached_at", sa.DateTime(timezone=True), nullable=True),
+        # Custom overrides
+        sa.Column("custom_orders_limit", sa.Integer(), nullable=True),
+        sa.Column("custom_products_limit", sa.Integer(), nullable=True),
+        sa.Column("custom_team_limit", sa.Integer(), nullable=True),
+        # Payment (future Stripe integration)
+        sa.Column("stripe_customer_id", sa.String(length=100), nullable=True),
+        sa.Column("stripe_subscription_id", sa.String(length=100), nullable=True),
+        # Cancellation
+        sa.Column("cancelled_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("cancellation_reason", sa.Text(), nullable=True),
+        # Timestamps
+        sa.Column(
+            "created_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("(CURRENT_TIMESTAMP)"),
+            nullable=False,
+        ),
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            server_default=sa.text("(CURRENT_TIMESTAMP)"),
+            nullable=False,
+        ),
+        sa.ForeignKeyConstraint(
+            ["vendor_id"],
+            ["vendors.id"],
+        ),
+        sa.PrimaryKeyConstraint("id"),
+        sa.UniqueConstraint("vendor_id"),
+    )
+    op.create_index(
+        op.f("ix_vendor_subscriptions_id"),
+        "vendor_subscriptions",
+        ["id"],
+        unique=False,
+    )
+    op.create_index(
+        op.f("ix_vendor_subscriptions_vendor_id"),
+        "vendor_subscriptions",
+        ["vendor_id"],
+        unique=True,
+    )
+    op.create_index(
+        op.f("ix_vendor_subscriptions_tier"),
+        "vendor_subscriptions",
+        ["tier"],
+        unique=False,
+    )
+    op.create_index(
+        op.f("ix_vendor_subscriptions_status"),
+        "vendor_subscriptions",
+        ["status"],
+        unique=False,
+    )
+    op.create_index(
+        op.f("ix_vendor_subscriptions_stripe_customer_id"),
+        "vendor_subscriptions",
+        ["stripe_customer_id"],
+        unique=False,
+    )
+    op.create_index(
+        op.f("ix_vendor_subscriptions_stripe_subscription_id"),
+        "vendor_subscriptions",
+        ["stripe_subscription_id"],
+        unique=False,
+    )
+    op.create_index(
+        "idx_subscription_vendor_status",
+        "vendor_subscriptions",
+        ["vendor_id", "status"],
+        unique=False,
+    )
+    op.create_index(
+        "idx_subscription_period",
+        "vendor_subscriptions",
+        ["period_start", "period_end"],
+        unique=False,
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("idx_subscription_period", table_name="vendor_subscriptions")
+    op.drop_index("idx_subscription_vendor_status", table_name="vendor_subscriptions")
+    op.drop_index(
+        op.f("ix_vendor_subscriptions_stripe_subscription_id"),
+        table_name="vendor_subscriptions",
+    )
+    op.drop_index(
+        op.f("ix_vendor_subscriptions_stripe_customer_id"),
+        table_name="vendor_subscriptions",
+    )
+    op.drop_index(
+        op.f("ix_vendor_subscriptions_status"), table_name="vendor_subscriptions"
+    )
+    op.drop_index(
+        op.f("ix_vendor_subscriptions_tier"), table_name="vendor_subscriptions"
+    )
+    op.drop_index(
+        op.f("ix_vendor_subscriptions_vendor_id"), table_name="vendor_subscriptions"
+    )
+    op.drop_index(
+        op.f("ix_vendor_subscriptions_id"), table_name="vendor_subscriptions"
+    )
+    op.drop_table("vendor_subscriptions")