feat: add platform marketing homepage with signup flow

Implement complete marketing homepage for Wizamart targeting Letzshop
vendors in Luxembourg. Includes:

- Marketing homepage with hero, pricing tiers, and add-ons
- 4-step signup wizard with Stripe card collection (30-day trial)
- Letzshop vendor lookup for shop claiming
- Platform API endpoints for pricing, vendors, and signup
- Stripe SetupIntent integration for trial with card upfront
- Database fields for Letzshop vendor identity tracking

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

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

alembic/versions/404b3e2d2865_add_letzshop_vendor_fields_and_trial_.py

@@ -0,0 +1,44 @@
+"""add_letzshop_vendor_fields_and_trial_tracking
+
+Revision ID: 404b3e2d2865
+Revises: l0a1b2c3d4e5
+Create Date: 2025-12-27 09:49:44.715243
+
+Adds:
+- vendors.letzshop_vendor_id - Link to Letzshop marketplace profile
+- vendors.letzshop_vendor_slug - Letzshop shop URL slug
+- vendor_subscriptions.card_collected_at - Track when card was collected for trial
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '404b3e2d2865'
+down_revision: Union[str, None] = 'l0a1b2c3d4e5'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # Add Letzshop vendor identity fields to vendors table
+    op.add_column('vendors', sa.Column('letzshop_vendor_id', sa.String(length=100), nullable=True))
+    op.add_column('vendors', sa.Column('letzshop_vendor_slug', sa.String(length=200), nullable=True))
+    op.create_index(op.f('ix_vendors_letzshop_vendor_id'), 'vendors', ['letzshop_vendor_id'], unique=True)
+    op.create_index(op.f('ix_vendors_letzshop_vendor_slug'), 'vendors', ['letzshop_vendor_slug'], unique=False)
+
+    # Add card collection tracking to vendor_subscriptions
+    op.add_column('vendor_subscriptions', sa.Column('card_collected_at', sa.DateTime(timezone=True), nullable=True))
+
+
+def downgrade() -> None:
+    # Remove card collection tracking from vendor_subscriptions
+    op.drop_column('vendor_subscriptions', 'card_collected_at')
+
+    # Remove Letzshop vendor identity fields from vendors
+    op.drop_index(op.f('ix_vendors_letzshop_vendor_slug'), table_name='vendors')
+    op.drop_index(op.f('ix_vendors_letzshop_vendor_id'), table_name='vendors')
+    op.drop_column('vendors', 'letzshop_vendor_slug')
+    op.drop_column('vendors', 'letzshop_vendor_id')