fix: Email rendering - newlines, hero text color, and card borders

🐛 Three Critical Email Issues Fixed:

1. Newlines Not Working
   ❌ "Order Number: #359 Order Total: Rp129.000" on same line
   ✅ Fixed by adding <br> for line continuations in paragraphs

   Key change in MarkdownParser.php:
   - Accumulate paragraph content with <br> between lines
   - Match TypeScript behavior exactly
   - Protect variables from markdown parsing

   Before:
   $paragraph_content = $trimmed;

   After:
   if ($paragraph_content) {
       $paragraph_content .= '<br>' . $trimmed;
   } else {
       $paragraph_content = $trimmed;
   }

2. Hero Card Text Color
   ❌ Heading black instead of white in Gmail
   ✅ Add inline color styles to all headings/paragraphs

   Problem: Gmail doesn't inherit color from parent
   Solution: Add style="color: white;" to each element

   $content = preg_replace(
       '/<(h[1-6]|p)([^>]*)>/',
       '<$1$2 style="color: ' . $hero_text_color . ';">',
       $content
   );

3. Blue Border on Cards
   ❌ Unwanted blue border in Gmail (screenshot 2)
   ✅ Removed borders from .card-info, .card-warning, .card-success

   Problem: CSS template had borders
   Solution: Removed border declarations

   Before:
   .card-info { border: 1px solid #0071e3; }

   After:
   .card-info { background-color: #f0f7ff; }

�� Additional Improvements:
- Variable protection during markdown parsing
- Don't match bold/italic across newlines
- Proper list handling
- Block-level tag detection
- Paragraph accumulation with line breaks

🎯 Result:
- ✅ Proper line breaks in paragraphs
- ✅ White text in hero cards (Gmail compatible)
- ✅ No unwanted borders
- ✅ Variables preserved during parsing
- ✅ Professional email appearance

Test: Create order, check email - should now show:
- Order Number: #359
- Order Total: Rp129.000
- Estimated Delivery: 3-5 business days
(Each on separate line with proper spacing)

includes/Core/Notifications/EmailRenderer.php

@@ -311,6 +311,13 @@ class EmailRenderer {
 					esc_attr($hero_gradient_end)
 				);
 				$content_style .= sprintf(' color: %s;', esc_attr($hero_text_color));
+				
+				// Add inline color to all headings and paragraphs for email client compatibility
+				$content = preg_replace(
+					'/<(h[1-6]|p)([^>]*)>/',
+					'<$1$2 style="color: ' . esc_attr($hero_text_color) . ';">',
+					$content
+				);
 			}
 		}