feat: add email settings with database overrides for admin and vendor

Platform Email Settings (Admin):
- Add GET/PUT/DELETE /admin/settings/email/* endpoints
- Settings stored in admin_settings table override .env values
- Support all providers: SMTP, SendGrid, Mailgun, Amazon SES
- Edit mode UI with provider-specific configuration forms
- Reset to .env defaults functionality
- Test email to verify configuration

Vendor Email Settings:
- Add VendorEmailSettings model with one-to-one vendor relationship
- Migration: v0a1b2c3d4e5_add_vendor_email_settings.py
- Service: vendor_email_settings_service.py with tier validation
- API endpoints: /vendor/email-settings/* (CRUD, status, verify)
- Email tab in vendor settings page with full configuration
- Warning banner until email is configured (like billing warnings)
- Premium providers (SendGrid, Mailgun, SES) tier-gated to Business+

Email Service Updates:
- get_platform_email_config(db) checks DB first, then .env
- Configurable provider classes accept config dict
- EmailService uses database-aware providers
- Vendor emails use vendor's own SMTP (Wizamart doesn't pay)
- "Powered by Wizamart" footer for Essential/Professional tiers
- White-label (no footer) for Business/Enterprise tiers

Other:
- Add scripts/install.py for first-time platform setup
- Add make install target
- Update init-prod to include email template seeding

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

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

models/database/__init__.py

@@ -21,6 +21,7 @@ from .customer import Customer, CustomerAddress
 from .password_reset_token import PasswordResetToken
 from .email import EmailCategory, EmailLog, EmailStatus, EmailTemplate
 from .vendor_email_template import VendorEmailTemplate
+from .vendor_email_settings import EmailProvider, VendorEmailSettings, PREMIUM_EMAIL_PROVIDERS
 from .feature import Feature, FeatureCategory, FeatureCode, FeatureUILocation
 from .inventory import Inventory
 from .inventory_transaction import InventoryTransaction, TransactionType
@@ -114,6 +115,9 @@ __all__ = [
     "EmailStatus",
     "EmailTemplate",
     "VendorEmailTemplate",
+    "VendorEmailSettings",
+    "EmailProvider",
+    "PREMIUM_EMAIL_PROVIDERS",
     # Features
     "Feature",
     "FeatureCategory",