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/MarkdownParser.php

@@ -0,0 +1,142 @@
+<?php
+/**
+ * Markdown to Email HTML Parser
+ * 
+ * PHP port of the TypeScript markdown parser from admin-spa
+ * 
+ * Supports:
+ * - Standard Markdown (headings, bold, italic, lists, links, horizontal rules)
+ * - Card blocks with ::: syntax
+ * - Button blocks with [button url="..."]Text[/button] syntax
+ * - Variables with {variable_name}
+ * - Checkmarks (✓) and bullet points (•)
+ * - Proper newline handling
+ * 
+ * @package WooNooW\Core\Notifications
+ */
+
+namespace WooNooW\Core\Notifications;
+
+class MarkdownParser {
+	
+	/**
+	 * Parse markdown to email HTML
+	 * 
+	 * @param string $markdown
+	 * @return string
+	 */
+	public static function parse($markdown) {
+		$html = $markdown;
+		
+		// Parse card blocks first (:::card or :::card[type])
+		$html = preg_replace_callback(
+			'/:::card(?:\[(\w+)\])?\n([\s\S]*?):::/s',
+			function($matches) {
+				$type = $matches[1] ?? '';
+				$content = trim($matches[2]);
+				$parsed_content = self::parse_basics($content);
+				return '[card' . ($type ? ' type="' . $type . '"' : '') . "]\n" . $parsed_content . "\n[/card]";
+			},
+			$html
+		);
+		
+		// Parse button blocks [button url="..."]Text[/button] - already in correct format
+		// Also support legacy [button](url){text} syntax
+		$html = preg_replace_callback(
+			'/\[button(?:\s+style="(solid|outline)")?\]\((.*?)\)\s*\{([^}]+)\}/',
+			function($matches) {
+				$style = $matches[1] ?? '';
+				$url = $matches[2];
+				$text = $matches[3];
+				return '[button url="' . $url . '"' . ($style ? ' style="' . $style . '"' : '') . ']' . $text . '[/button]';
+			},
+			$html
+		);
+		
+		// Horizontal rules
+		$html = preg_replace('/^---$/m', '<hr>', $html);
+		
+		// Parse remaining markdown (outside cards)
+		$html = self::parse_basics($html);
+		
+		return $html;
+	}
+	
+	/**
+	 * Parse basic markdown syntax
+	 * 
+	 * @param string $text
+	 * @return string
+	 */
+	private static function parse_basics($text) {
+		$html = $text;
+		
+		// Headings (must be done in order from h4 to h1 to avoid conflicts)
+		$html = preg_replace('/^#### (.*)$/m', '<h4>$1</h4>', $html);
+		$html = preg_replace('/^### (.*)$/m', '<h3>$1</h3>', $html);
+		$html = preg_replace('/^## (.*)$/m', '<h2>$1</h2>', $html);
+		$html = preg_replace('/^# (.*)$/m', '<h1>$1</h1>', $html);
+		
+		// Bold
+		$html = preg_replace('/\*\*(.*?)\*\*/s', '<strong>$1</strong>', $html);
+		$html = preg_replace('/__(.*?)__/s', '<strong>$1</strong>', $html);
+		
+		// Italic
+		$html = preg_replace('/\*([^\*]+?)\*/', '<em>$1</em>', $html);
+		$html = preg_replace('/_([^_]+?)_/', '<em>$1</em>', $html);
+		
+		// Links (but not button syntax)
+		$html = preg_replace('/\[(?!button)([^\]]+)\]\(([^)]+)\)/', '<a href="$2">$1</a>', $html);
+		
+		// Unordered lists (including checkmarks and bullets)
+		$html = preg_replace('/^[\*\-•✓✔] (.*)$/m', '<li>$1</li>', $html);
+		
+		// Wrap consecutive <li> in <ul>
+		$html = preg_replace('/(<li>.*?<\/li>\s*)+/s', '<ul>$0</ul>', $html);
+		
+		// Ordered lists
+		$html = preg_replace('/^\d+\. (.*)$/m', '<li>$1</li>', $html);
+		
+		// Paragraphs (lines not already in tags)
+		$lines = explode("\n", $html);
+		$processed_lines = [];
+		
+		foreach ($lines as $line) {
+			$trimmed = trim($line);
+			
+			// Skip empty lines
+			if (empty($trimmed)) {
+				$processed_lines[] = '';
+				continue;
+			}
+			
+			// Skip lines that are already HTML tags or shortcodes
+			if (preg_match('/^</', $trimmed) || preg_match('/^\[/', $trimmed)) {
+				$processed_lines[] = $line;
+				continue;
+			}
+			
+			// Wrap in paragraph
+			$processed_lines[] = '<p>' . $line . '</p>';
+		}
+		
+		$html = implode("\n", $processed_lines);
+		
+		// Clean up extra newlines in HTML
+		$html = preg_replace('/\n{3,}/', "\n\n", $html);
+		
+		return $html;
+	}
+	
+	/**
+	 * Convert newlines to <br> tags for email rendering
+	 * 
+	 * @param string $html
+	 * @return string
+	 */
+	public static function nl2br_email($html) {
+		// Don't convert newlines inside HTML tags
+		$html = preg_replace('/(?<!>)\n(?!<)/', '<br>', $html);
+		return $html;
+	}
+}