feat: add knowledge version history (closes #75, closes #76)

- Added EntryVersion model with author relation
- Implemented automatic versioning on entry create/update
- Added API endpoints for version history:
  - GET /api/knowledge/entries/:slug/versions - list versions
  - GET /api/knowledge/entries/:slug/versions/:version - get specific
  - POST /api/knowledge/entries/:slug/restore/:version - restore version
- Created VersionHistory.tsx component with timeline view
- Added History tab to entry detail page
- Supports version viewing and restoring
- Includes comprehensive tests for version operations
- All TypeScript types are explicit and type-safe

apps/web/src/app/(authenticated)/knowledge/[slug]/page.tsx

@@ -7,6 +7,7 @@ import { EntryStatus, Visibility } from "@mosaic/shared";
 import { EntryViewer } from "@/components/knowledge/EntryViewer";
 import { EntryEditor } from "@/components/knowledge/EntryEditor";
 import { EntryMetadata } from "@/components/knowledge/EntryMetadata";
+import { VersionHistory } from "@/components/knowledge/VersionHistory";
 import { fetchEntry, updateEntry, deleteEntry, fetchTags } from "@/lib/api/knowledge";
 
 /**
@@ -32,6 +33,7 @@ export default function EntryPage() {
   const [editTags, setEditTags] = useState<string[]>([]);
   const [availableTags, setAvailableTags] = useState<KnowledgeTag[]>([]);
   const [hasUnsavedChanges, setHasUnsavedChanges] = useState(false);
+  const [activeTab, setActiveTab] = useState<"content" | "history">("content");
 
   // Load entry data
   useEffect(() => {
@@ -179,6 +181,25 @@ export default function EntryPage() {
     }
   };
 
+  const handleVersionRestore = (): void => {
+    // Reload entry after version restore
+    async function reload(): Promise<void> {
+      try {
+        const data = await fetchEntry(slug);
+        setEntry(data);
+        setEditTitle(data.title);
+        setEditContent(data.content);
+        setEditStatus(data.status);
+        setEditVisibility(data.visibility);
+        setEditTags(data.tags.map((tag) => tag.id));
+        setActiveTab("content");
+      } catch (err) {
+        setError(err instanceof Error ? err.message : "Failed to reload entry");
+      }
+    }
+    void reload();
+  };
+
   if (isLoading) {
     return (
       <div className="max-w-4xl mx-auto p-6">
@@ -268,12 +289,44 @@ export default function EntryPage() {
         </div>
       )}
 
+      {/* Tabs */}
+      {!isEditing && (
+        <div className="mb-6 border-b border-gray-200 dark:border-gray-700">
+          <nav className="flex gap-6">
+            <button
+              type="button"
+              onClick={() => setActiveTab("content")}
+              className={`pb-3 border-b-2 font-medium text-sm transition-colors ${
+                activeTab === "content"
+                  ? "border-blue-600 text-blue-600 dark:text-blue-400"
+                  : "border-transparent text-gray-500 dark:text-gray-400 hover:text-gray-700 dark:hover:text-gray-300"
+              }`}
+            >
+              Content
+            </button>
+            <button
+              type="button"
+              onClick={() => setActiveTab("history")}
+              className={`pb-3 border-b-2 font-medium text-sm transition-colors ${
+                activeTab === "history"
+                  ? "border-blue-600 text-blue-600 dark:text-blue-400"
+                  : "border-transparent text-gray-500 dark:text-gray-400 hover:text-gray-700 dark:hover:text-gray-300"
+              }`}
+            >
+              History
+            </button>
+          </nav>
+        </div>
+      )}
+
       {/* Content */}
       <div className="mb-6">
         {isEditing ? (
           <EntryEditor content={editContent} onChange={setEditContent} />
-        ) : (
+        ) : activeTab === "content" ? (
           <EntryViewer entry={entry} />
+        ) : (
+          <VersionHistory slug={slug} onRestore={handleVersionRestore} />
         )}
       </div>