fix: Add markdown parsing, variable replacement, and logo fallback

🐛 Email Rendering Issues Fixed:

1. Markdown Not Parsed
   ❌ Raw markdown showing: ## Great news...
   ✅ Created MarkdownParser.php (PHP port from TypeScript)
   ✅ Parses headings, bold, italic, lists, links
   ✅ Supports card blocks and button syntax
   ✅ Proper newline handling

2. Variables Not Replaced
   ❌ {support_email} showing literally
   ✅ Added support_email variable
   ✅ Added current_year variable
   ✅ Added estimated_delivery variable (3-5 business days)

3. Broken Logo Image
   ❌ Broken image placeholder
   ✅ Fallback to site icon if no logo set
   ✅ Fallback to text header if no icon
   ✅ Proper URL handling

4. Newline Issues
   ❌ Variables on same line
   ✅ Markdown parser handles newlines correctly
   ✅ Proper paragraph wrapping

📦 New File:
- includes/Core/Notifications/MarkdownParser.php
  - parse() - Convert markdown to HTML
  - parse_basics() - Parse standard markdown
  - nl2br_email() - Convert newlines for email

🔧 Updated Files:
- EmailRenderer.php
  - Use MarkdownParser in render_card()
  - Add support_email, current_year variables
  - Add estimated_delivery calculation
  - Logo fallback to site icon
  - Text header fallback if no logo

🎯 Result:
- ✅ Markdown properly rendered
- ✅ All variables replaced
- ✅ Logo displays (or text fallback)
- ✅ Proper line breaks
- ✅ Professional email appearance

📝 Example:
Before: ## Great news, {customer_name}!
After: <h2>Great news, Dwindi Ramadhana!</h2>

Before: {support_email}
After: admin@example.com

Before: Broken image
After: Site icon or store name

includes/Core/Notifications/EmailRenderer.php

@@ -143,10 +143,15 @@ class EmailRenderer {
 			'store_name' => get_bloginfo('name'),
 			'store_url' => home_url(),
 			'site_title' => get_bloginfo('name'),
+			'support_email' => get_option('admin_email'),
+			'current_year' => date('Y'),
 		];
 		
 		// Order variables
 		if ($data instanceof \WC_Order) {
+			// Calculate estimated delivery (3-5 business days from now)
+			$estimated_delivery = date('F j', strtotime('+3 days')) . '-' . date('j', strtotime('+5 days'));
+			
 			$variables = array_merge($variables, [
 				'order_number' => $data->get_order_number(),
 				'order_id' => $data->get_id(),
@@ -160,6 +165,7 @@ class EmailRenderer {
 				'order_url' => $data->get_view_order_url(),
 				'payment_method' => $data->get_payment_method_title(),
 				'shipping_method' => $data->get_shipping_method(),
+				'estimated_delivery' => $estimated_delivery,
 				'customer_name' => $data->get_formatted_billing_full_name(),
 				'customer_first_name' => $data->get_billing_first_name(),
 				'customer_last_name' => $data->get_billing_last_name(),
@@ -280,6 +286,9 @@ class EmailRenderer {
 		$type = $attributes['type'] ?? 'default';
 		$bg = $attributes['bg'] ?? null;
 		
+		// Parse markdown in content
+		$content = MarkdownParser::parse($content);
+		
 		// Get email customization settings for colors
 		$email_settings = get_option('woonoow_email_settings', []);
 		$hero_gradient_start = $email_settings['hero_gradient_start'] ?? '#667eea';
@@ -397,14 +406,22 @@ class EmailRenderer {
 		$body_bg = '#f8f8f8';
 		
 		// Email header (logo or text)
-		if (!empty($email_settings['logo_url'])) {
+		$logo_url = $email_settings['logo_url'] ?? '';
+		
+		// Fallback to site icon if no logo set
+		if (empty($logo_url) && has_site_icon()) {
+			$logo_url = get_site_icon_url(200);
+		}
+		
+		if (!empty($logo_url)) {
 			$header = sprintf(
 				'<a href="%s"><img src="%s" alt="%s" style="max-width: 200px; max-height: 60px;"></a>',
 				esc_url($variables['store_url']),
-				esc_url($email_settings['logo_url']),
+				esc_url($logo_url),
 				esc_attr($variables['store_name'])
 			);
 		} else {
+			// No logo, use text header
 			$header_text = !empty($email_settings['header_text']) ? $email_settings['header_text'] : $variables['store_name'];
 			$header = sprintf(
 				'<a href="%s" style="font-size: 24px; font-weight: 700; color: #333; text-decoration: none;">%s</a>',