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/yarn.lock

@@ -452,6 +452,11 @@
   resolved "https://registry.npmjs.org/@types/deep-eql/-/deep-eql-4.0.2.tgz"
   integrity sha512-c9h9dVVMigMPc4bwTvC5dxqtqJZwQPePsWjPlpSOnojbor6pGqdk541lfA7AqFQr5pB1BRdq0juY9db81BwyFw==
 
+"@types/diff@^7.0.2":
+  version "7.0.2"
+  resolved "https://registry.npmjs.org/@types/diff/-/diff-7.0.2.tgz"
+  integrity sha512-JSWRMozjFKsGlEjiiKajUjIJVKuKdE3oVy2DNtK+fUo8q82nhFZ2CPQwicAIkXrofahDXrWJ7mjelvZphMS98Q==
+
 "@types/estree@*", "@types/estree@^1.0.0", "@types/estree@^1.0.5", "@types/estree@^1.0.6", "@types/estree@1.0.8":
   version "1.0.8"
   resolved "https://registry.npmjs.org/@types/estree/-/estree-1.0.8.tgz"
@@ -888,6 +893,11 @@ devalue@^5.6.4:
   resolved "https://registry.npmjs.org/devalue/-/devalue-5.6.4.tgz"
   integrity sha512-Gp6rDldRsFh/7XuouDbxMH3Mx8GMCcgzIb1pDTvNyn8pZGQ22u+Wa+lGV9dQCltFQ7uVw0MhRyb8XDskNFOReA==
 
+diff@^8.0.3:
+  version "8.0.3"
+  resolved "https://registry.npmjs.org/diff/-/diff-8.0.3.tgz"
+  integrity sha512-qejHi7bcSD4hQAZE0tNAawRK1ZtafHDmMTMkrrIGgSLl7hTnQHmKCeB45xAcbfTqK2zowkM3j3bHt/4b/ARbYQ==
+
 enhanced-resolve@^5.19.0:
   version "5.20.0"
   resolved "https://registry.npmjs.org/enhanced-resolve/-/enhanced-resolve-5.20.0.tgz"