Add WYSIWYG Markdown editor (EasyMDE) to wiki pages

Reusable MarkdownEditor component using EasyMDE:
- Toolbar: bold, italic, headings, quotes, lists, links, images,
  tables, code blocks, preview, side-by-side, fullscreen
- Dark mode support with custom CSS overrides
- Value syncs via bind:value for form submission
- Applied to both wiki new and edit pages
- Replaces the plain textarea + manual preview toggle

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -23,6 +23,7 @@
 		"date-fns": "^4.1.0",
 		"dotenv": "^17.4.1",
 		"drizzle-orm": "^0.38.4",
+		"easymde": "^2.20.0",
 		"marked": "^18.0.0",
 		"pg": "^8.13.1",
 		"qrcode": "^1.5.4",