feat(artifacts): capture Claude Docs docs and session documents, claim unowned rows

- A Claude Docs `batch` that creates a doc is captured like an `Artifact`
  publish, titled by the doc's name and linked by its own frame URL.
- At Stop/SessionEnd, each pptx/docx/xlsx/pdf/html a workspace session
  created or changed is snapshotted into its owner's library (`auto`);
  an unchanged file is skipped, a changed one refreshes its snapshot.
- Server mode: a page with no owner carries a suggested owner (the
  workspace or home its session ran in). The suggested user claims or
  declines it; an admin claims or assigns any. New tab Unowned /
  Is this yours? on the Artifacts page; all three actions audited.

server/openapi-extra/artifacts.js

@@ -82,7 +82,11 @@ const paths = {
       description:
         "A developer sees their own rows plus shared ones; staff see every row in `hub` scope.",
       parameters: [
-        { name: "scope", in: "query", schema: { type: "string", enum: ["mine", "hub"] } },
+        {
+          name: "scope",
+          in: "query",
+          schema: { type: "string", enum: ["all", "mine", "hub", "unowned"] },
+        },
         { name: "kind", in: "query", schema: { type: "string", enum: ["page", "file", "skill", "plugin"] } },
         { name: "q", in: "query", schema: { type: "string" } },
         laneQuery,