chore(deps): install Tiptap 3.22.5 (core, starter-kit, extension-mention)

Exact version pins — all three packages share ProseMirror peer deps and must
stay in sync. Renovate grouping in renovate.json ensures they bump together.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/package.json

@@ -21,6 +21,9 @@
 		"generate:api": "openapi-typescript http://localhost:8080/v3/api-docs -o ./src/lib/generated/api.ts"
 	},
 	"dependencies": {
+		"@tiptap/core": "3.22.5",
+		"@tiptap/extension-mention": "3.22.5",
+		"@tiptap/starter-kit": "3.22.5",
 		"diff": "^8.0.3",
 		"openapi-fetch": "^0.13.5",
 		"pdfjs-dist": "^5.5.207"