feat: Card-based email system implementation

## ✅ Core Card System Complete!

### base.html Template
- ✅ Single, theme-agnostic template
- ✅ Card system CSS (default, highlight, info, warning, success, bg)
- ✅ Customizable header (logo/text)
- ✅ Customizable footer + social icons
- ✅ Customizable body background
- ✅ Mobile responsive
- ✅ Email client compatible (Outlook, Gmail, etc.)

### EmailRenderer.php - Card Parser
- ✅ `parse_cards()` - Parses [card]...[/card] syntax
- ✅ `parse_card_attributes()` - Extracts type and bg attributes
- ✅ `render_card()` - Renders card HTML
- ✅ `render_card_spacing()` - 24px spacing between cards
- ✅ `render_html()` - Email customization support
- ✅ `get_social_icon_url()` - Social media icons

### Card Types Supported
```
[card]                        → Default white card
[card type="highlight"]       → Purple gradient card
[card type="info"]            → Blue info card
[card type="warning"]         → Yellow warning card
[card type="success"]         → Green success card
[card bg="https://..."]       → Background image card
```

### Email Customization
- ✅ Header: Logo or text
- ✅ Body background color
- ✅ Footer text
- ✅ Social media links (Facebook, Instagram, Twitter, LinkedIn)
- ✅ Stored in `woonoow_notification_settings[email_appearance]`

### Default Templates Updated
- ✅ order_placed_email - Multi-card layout
- ✅ order_processing_email - Success card + summary
- ✅ Other templates ready to update

---

**Architecture:**
```
Content with [card] tags
    ↓
parse_cards()
    ↓
render_card() × N
    ↓
base.html template
    ↓
Beautiful HTML email! 🎨
```

**Next:** Settings UI + Live Preview 🚀

includes/Core/Notifications/TemplateProvider.php

@@ -143,7 +143,26 @@ class TemplateProvider {
 				'event_id' => 'order_placed',
 				'channel_id' => 'email',
 				'subject' => $wc_new_order['subject'] ?? __('New Order #{order_number}', 'woonoow'),
-				'body' => __("Hi Admin,\n\nYou have received a new order.\n\nOrder Number: {order_number}\nOrder Total: {order_total}\nCustomer: {customer_name}\nEmail: {customer_email}\n\nView order: {order_url}", 'woonoow'),
+				'body' => __('[card]
+<h1>New Order Received</h1>
+<p>Hi Admin,</p>
+<p>You have received a new order from <strong>{customer_name}</strong>.</p>
+<div class="info-box">
+	<p style="margin: 0;"><strong>Order #{order_number}</strong></p>
+	<p style="margin: 0;">Total: {order_total}</p>
+</div>
+[/card]
+
+[card]
+<h2>Customer Details</h2>
+<p><strong>Name:</strong> {customer_name}<br>
+<strong>Email:</strong> {customer_email}<br>
+<strong>Phone:</strong> {customer_phone}</p>
+[/card]
+
+[card]
+<p style="text-align: center;"><a href="{order_url}" class="button">View Order Details</a></p>
+[/card]', 'woonoow'),
 				'variables' => self::get_order_variables(),
 				'wc_email_id' => 'WC_Email_New_Order',
 			],
@@ -151,7 +170,26 @@ class TemplateProvider {
 				'event_id' => 'order_processing',
 				'channel_id' => 'email',
 				'subject' => $wc_processing['subject'] ?? __('Your order #{order_number} is being processed', 'woonoow'),
-				'body' => __("Hi {customer_name},\n\nThank you for your order! We're now processing it.\n\nOrder Number: {order_number}\nOrder Total: {order_total}\nPayment Method: {payment_method}\n\nYou can track your order here: {order_url}\n\nBest regards,\n{store_name}", 'woonoow'),
+				'body' => __('[card type="success"]
+<h1>✅ Order Confirmed!</h1>
+<p>Hi {customer_name},</p>
+<p>Thank you for your order! We\'re now processing it and will notify you once it ships.</p>
+[/card]
+
+[card]
+<h2>Order Summary</h2>
+<div class="info-box">
+	<p style="margin: 0;"><strong>Order #{order_number}</strong></p>
+	<p style="margin: 0;">Total: {order_total}</p>
+	<p style="margin: 0;">Payment: {payment_method}</p>
+</div>
+{order_items}
+[/card]
+
+[card]
+<p style="text-align: center;"><a href="{order_url}" class="button">Track Your Order</a></p>
+<p style="text-align: center; font-size: 14px; color: #888;">Questions? Reply to this email or contact us.</p>
+[/card]', 'woonoow'),
 				'variables' => self::get_order_variables(),
 				'wc_email_id' => 'WC_Email_Customer_Processing_Order',
 			],