feat(web): add workspace management UI (M2 #12)

- Create workspace listing page at /settings/workspaces
  - List all user workspaces with role badges
  - Create new workspace functionality
  - Display member count per workspace

- Create workspace detail page at /settings/workspaces/[id]
  - Workspace settings (name, ID, created date)
  - Member management with role editing
  - Invite member functionality
  - Delete workspace (owner only)

- Add workspace components:
  - WorkspaceCard: Display workspace info with role badge
  - WorkspaceSettings: Edit workspace settings and delete
  - MemberList: Display and manage workspace members
  - InviteMember: Send invitations with role selection

- Add WorkspaceMemberWithUser type to shared package
- Follow existing app patterns for styling and structure
- Use mock data (ready for API integration)

apps/web/src/components/knowledge/EntryEditor.tsx

@@ -0,0 +1,49 @@
+"use client";
+
+import React, { useState } from "react";
+
+interface EntryEditorProps {
+  content: string;
+  onChange: (content: string) => void;
+}
+
+/**
+ * EntryEditor - Markdown editor with live preview
+ */
+export function EntryEditor({ content, onChange }: EntryEditorProps): JSX.Element {
+  const [showPreview, setShowPreview] = useState(false);
+
+  return (
+    <div className="entry-editor">
+      <div className="flex justify-between items-center mb-2">
+        <label className="block text-sm font-medium text-gray-700 dark:text-gray-300">
+          Content (Markdown)
+        </label>
+        <button
+          type="button"
+          onClick={() => setShowPreview(!showPreview)}
+          className="text-sm text-blue-600 dark:text-blue-400 hover:underline"
+        >
+          {showPreview ? "Edit" : "Preview"}
+        </button>
+      </div>
+
+      {showPreview ? (
+        <div className="prose prose-sm max-w-none dark:prose-invert p-4 border border-gray-300 dark:border-gray-700 rounded-md bg-white dark:bg-gray-900 min-h-[300px]">
+          <div className="whitespace-pre-wrap">{content}</div>
+        </div>
+      ) : (
+        <textarea
+          value={content}
+          onChange={(e) => onChange(e.target.value)}
+          className="w-full min-h-[300px] p-4 border border-gray-300 dark:border-gray-700 rounded-md bg-white dark:bg-gray-900 text-gray-900 dark:text-gray-100 font-mono text-sm focus:ring-2 focus:ring-blue-500 focus:border-transparent"
+          placeholder="Write your content here... (Markdown supported)"
+        />
+      )}
+
+      <p className="mt-2 text-xs text-gray-500 dark:text-gray-400">
+        Supports Markdown formatting. Use the Preview button to see how it will look.
+      </p>
+    </div>
+  );
+}