feat(frontend): add document history panel with diff and compare mode

Adds a collapsible history section to the document detail view, showing
all saved versions with changed-field labels, word-level diff between
adjacent versions, and a compare mode for any two arbitrary versions.

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

frontend/package-lock.json

@@ -8,6 +8,7 @@
 			"name": "frontend",
 			"version": "0.0.1",
 			"dependencies": {
+				"diff": "^8.0.3",
 				"openapi-fetch": "^0.13.5"
 			},
 			"devDependencies": {
@@ -21,6 +22,7 @@
 				"@tailwindcss/forms": "^0.5.10",
 				"@tailwindcss/typography": "^0.5.19",
 				"@tailwindcss/vite": "^4.1.17",
+				"@types/diff": "^7.0.2",
 				"@types/node": "^24",
 				"@vitest/browser-playwright": "^4.0.10",
 				"eslint": "^9.39.1",
@@ -1895,6 +1897,13 @@
 			"dev": true,
 			"license": "MIT"
 		},
+		"node_modules/@types/diff": {
+			"version": "7.0.2",
+			"resolved": "https://registry.npmjs.org/@types/diff/-/diff-7.0.2.tgz",
+			"integrity": "sha512-JSWRMozjFKsGlEjiiKajUjIJVKuKdE3oVy2DNtK+fUo8q82nhFZ2CPQwicAIkXrofahDXrWJ7mjelvZphMS98Q==",
+			"dev": true,
+			"license": "MIT"
+		},
 		"node_modules/@types/estree": {
 			"version": "1.0.8",
 			"resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.8.tgz",
@@ -2780,6 +2789,15 @@
 			"dev": true,
 			"license": "MIT"
 		},
+		"node_modules/diff": {
+			"version": "8.0.3",
+			"resolved": "https://registry.npmjs.org/diff/-/diff-8.0.3.tgz",
+			"integrity": "sha512-qejHi7bcSD4hQAZE0tNAawRK1ZtafHDmMTMkrrIGgSLl7hTnQHmKCeB45xAcbfTqK2zowkM3j3bHt/4b/ARbYQ==",
+			"license": "BSD-3-Clause",
+			"engines": {
+				"node": ">=0.3.1"
+			}
+		},
 		"node_modules/enhanced-resolve": {
 			"version": "5.20.0",
 			"resolved": "https://registry.npmjs.org/enhanced-resolve/-/enhanced-resolve-5.20.0.tgz",