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/lib/git-diff.js

@@ -1350,6 +1350,7 @@ module.exports = {
   laneStatus,
   listCommits,
   listPaths,
+  lsFiles,
   listTree,
   listTreeAll,
   parseNumstat,
@@ -1358,6 +1359,7 @@ module.exports = {
   readFileAt,
   readImageAt,
   resolveBaseRef,
+  walkFolder,
   defaultBranch,
   DEFAULT_CONTEXT,
   MAX_CONTEXT,