chore(deps): add HTML sanitizers for Geschichten rich-text body

Adds OWASP Java HTML Sanitizer on the backend and DOMPurify on the frontend.
Together with Tiptap on the writer side they form a defense-in-depth chain
against XSS in the new Geschichte body field (issue #381).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/package-lock.json

@@ -12,6 +12,7 @@
 				"@tiptap/extension-mention": "3.22.5",
 				"@tiptap/starter-kit": "3.22.5",
 				"diff": "^8.0.3",
+				"dompurify": "^3.4.2",
 				"openapi-fetch": "^0.13.5",
 				"pdfjs-dist": "^5.5.207"
 			},
@@ -28,6 +29,7 @@
 				"@tailwindcss/typography": "^0.5.19",
 				"@tailwindcss/vite": "^4.1.17",
 				"@types/diff": "^7.0.2",
+				"@types/dompurify": "^3.0.5",
 				"@types/node": "^24",
 				"@vitest/browser-playwright": "^4.0.10",
 				"@vitest/coverage-v8": "^4.1.0",
@@ -2620,6 +2622,16 @@
 			"dev": true,
 			"license": "MIT"
 		},
+		"node_modules/@types/dompurify": {
+			"version": "3.0.5",
+			"resolved": "https://registry.npmjs.org/@types/dompurify/-/dompurify-3.0.5.tgz",
+			"integrity": "sha512-1Wg0g3BtQF7sSb27fJQAKck1HECM6zV1EB66j8JH9i3LCjYabJa0FSdiSgsD5K/RbrsR0SiraKacLB+T8ZVYAg==",
+			"dev": true,
+			"license": "MIT",
+			"dependencies": {
+				"@types/trusted-types": "*"
+			}
+		},
 		"node_modules/@types/estree": {
 			"version": "1.0.8",
 			"resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.8.tgz",
@@ -2655,7 +2667,7 @@
 			"version": "2.0.7",
 			"resolved": "https://registry.npmjs.org/@types/trusted-types/-/trusted-types-2.0.7.tgz",
 			"integrity": "sha512-ScaPdn1dQczgbl0QFTeTOmVHFULt394XJgOQNoyVhZ6r2vLnMLJfBPd53SB52T/3G36VI1/g2MZaX0cwDuXsfw==",
-			"dev": true,
+			"devOptional": true,
 			"license": "MIT"
 		},
 		"node_modules/@typescript-eslint/eslint-plugin": {
@@ -3584,6 +3596,15 @@
 				"node": ">=0.3.1"
 			}
 		},
+		"node_modules/dompurify": {
+			"version": "3.4.2",
+			"resolved": "https://registry.npmjs.org/dompurify/-/dompurify-3.4.2.tgz",
+			"integrity": "sha512-lHeS9SA/IKeIFFyYciHBr2n0v1VMPlSj843HdLOwjb2OxNwdq9Xykxqhk+FE42MzAdHvInbAolSE4mhahPpjXA==",
+			"license": "(MPL-2.0 OR Apache-2.0)",
+			"optionalDependencies": {
+				"@types/trusted-types": "^2.0.7"
+			}
+		},
 		"node_modules/enhanced-resolve": {
 			"version": "5.20.0",
 			"resolved": "https://registry.npmjs.org/enhanced-resolve/-/enhanced-resolve-5.20.0.tgz",