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>

static/vendor/js/billing.js

@@ -189,7 +189,8 @@ function vendorBilling() {
         formatDate(dateString) {
             if (!dateString) return '-';
             const date = new Date(dateString);
-            return date.toLocaleDateString('en-US', {
+            const locale = window.VENDOR_CONFIG?.locale || 'en-GB';
+            return date.toLocaleDateString(locale, {
                 year: 'numeric',
                 month: 'short',
                 day: 'numeric'
@@ -199,9 +200,11 @@ function vendorBilling() {
         formatCurrency(cents, currency = 'EUR') {
             if (cents === null || cents === undefined) return '-';
             const amount = cents / 100;
-            return new Intl.NumberFormat('en-US', {
+            const locale = window.VENDOR_CONFIG?.locale || 'en-GB';
+            const currencyCode = window.VENDOR_CONFIG?.currency || currency;
+            return new Intl.NumberFormat(locale, {
                 style: 'currency',
-                currency: currency
+                currency: currencyCode
             }).format(amount);
         }
     };