feat: Complete markdown syntax refinement and variable protection

✅ New cleaner syntax implemented:
- [card:type] instead of [card type='type']
- [button:style](url)Text[/button] instead of [button url='...' style='...']
- Standard markdown images: ![alt](url)

✅ Variable protection from markdown parsing:
- Variables with underscores (e.g., {order_items_table}) now protected
- HTML comment placeholders prevent italic/bold parsing
- All variables render correctly in preview

✅ Button rendering fixes:
- Buttons work in Visual mode inside cards
- Buttons work in Preview mode
- Button clicks prevented in visual editor
- Proper styling for solid and outline buttons

✅ Backward compatibility:
- Old syntax still supported
- No breaking changes

✅ Bug fixes:
- Fixed order_item_table → order_items_table naming
- Fixed button regex to match across newlines
- Added button/image parsing to parseMarkdownBasics
- Prevented button clicks on .button and .button-outline classes

📚 Documentation:
- NEW_MARKDOWN_SYNTAX.md - Complete user guide
- MARKDOWN_SYNTAX_AND_VARIABLES.md - Technical analysis

CONVERTER_FIXES_SUMMARY.md

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+# Converter Fixes Summary
+
+## Issues Fixed
+
+### 1. ✅ Exact Event Naming - No Mapping
+
+**Problem:** API used `order_processing` but Email templates had `order_confirmed`. Required a "bridge" mapping.
+
+**Solution:** Renamed template methods to match API exactly:
+- `customer_order_confirmed()` → `customer_order_processing()`
+- `staff_order_confirmed()` → `staff_order_processing()`
+- `customer_registered()` → `customer_new_customer()`
+
+**Result:** Direct 1:1 mapping, no confusion, clean code.
+
+### 2. ✅ Markdown Converter Respects [card] Boundaries
+
+**Problem:** `markdownToBlocks()` was splitting by double newlines (`\n\n`), causing:
+- Raw `[/card]` tags left in output
+- Each line with double space became a new card
+- `##` headings not rendered
+
+**Root Cause:**
+```typescript
+// OLD - WRONG
+const sections = markdown.split(/\n\n+/);  // Splits by double newlines!
+```
+
+**Solution:** Parse by `[card]...[/card]` boundaries:
+```typescript
+// NEW - CORRECT
+while (remaining.length > 0) {
+  const cardMatch = remaining.match(/^\[card([^\]]*)\]([\s\S]*?)\[\/card\]/);
+  if (cardMatch) {
+    // Extract content between [card] and [/card]
+    const content = cardMatch[2].trim();
+    blocks.push({ type: 'card', content });
+    remaining = remaining.substring(cardMatch[0].length); // Advance!
+  }
+}
+```
+
+**Key Changes:**
+- Uses regex to find `[card]...[/card]` pairs
+- Extracts content between tags
+- Advances `remaining` string after each match
+- No splitting by newlines
+
+### 3. ⚠️ Markdown Rendering in Preview (Partial)
+
+**Current State:**
+- Markdown is stored in database: `## Heading\n\n**bold**`
+- Frontend CodeEditor shows clean markdown ✅
+- Preview shows markdown as-is (not converted to HTML) ❌
+
+**Why:**
+The preview uses `htmlContent` which contains `[card]## Heading[/card]` but doesn't convert the markdown inside to HTML.
+
+**Next Steps:**
+Backend PHP needs to convert markdown to HTML when rendering emails. The `[card]` shortcode handler should:
+1. Extract content
+2. Convert markdown to HTML
+3. Wrap in styled div
+
+## Files Modified
+
+1. `/includes/Email/DefaultTemplates.php`
+   - Renamed methods to match API event IDs exactly
+   - Updated subject keys
+
+2. `/includes/Core/Notifications/TemplateProvider.php`
+   - Removed event mapping
+   - Direct lookup: `$allEmailTemplates[$recipient_type][$event_id]`
+
+3. `/admin-spa/src/components/EmailBuilder/converter.ts`
+   - Fixed `markdownToBlocks()` to respect `[card]...[/card]` boundaries
+   - Added proper string advancement
+   - No more double-newline splitting
+
+## Testing Checklist
+
+- [x] Event names match between API and templates
+- [x] No mapping/bridging code
+- [x] Markdown editor shows clean markdown
+- [x] `[/card]` tags not left in output
+- [x] Double newlines don't create new cards
+- [ ] Preview renders markdown as HTML (needs backend fix)
+- [ ] Headings show as `<h2>` not `##` in preview
+- [ ] Line breaks work correctly in preview
+
+## Remaining Work
+
+**Backend Markdown Rendering:**
+The WordPress shortcode handler for `[card]` needs to convert markdown content to HTML before rendering.
+
+Location: Likely in `/includes/Email/` or `/includes/Core/Notifications/`
+
+Required: A function that processes `[card]` shortcodes and converts their markdown content to HTML using a markdown parser.