feat: enhance CMS editor with rich text features and fix line break preservation

- Fix line break preservation with proper HardBreak extension configuration
- Add text alignment support (left, center, right, justify) for paragraphs and headings
- Add H4-H6 heading support with keyboard shortcuts
- Add code block support with syntax highlighting for multiple languages
- Enhance preview functionality with split-pane view (Edit/Preview/Split modes)
- Add custom prose CSS overrides for proper content rendering
- Update DOMPurify configuration to preserve br tags and text alignment
- Add visual indicators and help modal with all keyboard shortcuts
- Improve toolbar organization with grouped buttons and separators
- Add auto-save status indicator and word/character count

Fixes issues with:
- Line breaks not showing in gallery view
- Limited heading options (only H1-H3)
- No text formatting capabilities
- Missing preview functionality

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "picpeak-frontend",
   "private": true,
-  "version": "1.0.58",
+  "version": "1.0.60",
   "type": "module",
   "scripts": {
     "dev": "vite",
@@ -12,10 +12,16 @@
   },
   "dependencies": {
     "@tanstack/react-query": "^5.0.0",
+    "@tiptap/extension-character-count": "^2.26.1",
+    "@tiptap/extension-code-block-lowlight": "^2.26.1",
+    "@tiptap/extension-hard-break": "^2.26.1",
     "@tiptap/extension-link": "^2.25.0",
+    "@tiptap/extension-placeholder": "^2.26.1",
+    "@tiptap/extension-text-align": "^2.26.1",
     "@tiptap/react": "^2.25.0",
     "@tiptap/starter-kit": "^2.25.0",
     "@types/dompurify": "^3.0.5",
+    "@types/lodash": "^4.17.20",
     "@types/react-google-recaptcha": "^2.1.9",
     "axios": "^1.3.2",
     "clsx": "^2.0.0",
@@ -25,6 +31,8 @@
     "i18next-browser-languagedetector": "^8.2.0",
     "i18next-http-backend": "^3.0.2",
     "js-cookie": "^3.0.5",
+    "lodash": "^4.17.21",
+    "lowlight": "^2.9.0",
     "lucide-react": "^0.292.0",
     "react": "^18.3.1",
     "react-countdown": "^2.3.5",