fix: v2.6.1 — panes start in their folder again after an update (#69), Changes panel stacks every repo, clickable paths in chat

- #69: tmux applies a pane's `-c` only while its server's own cwd exists.
  The server was forked from the dashboard's cwd (the plugin cache dir),
  outlives updates, and the old cache dir is pruned — after that every new
  pane started in a deleted directory, where `claude` died at once ("run not
  found") and a shell printed getcwd errors. tmux calls now run from `/`,
  and the pane's sh wrapper cds into its folder itself, which also heals a
  tmux server that is already stuck.
- Changes panel: a workspace's extra folders are sections stacked under the
  workspace folder (VS Code Source Control style), with Close repository /
  Close other repositories on a header's right-click.
- Chat: URLs and absolute paths are links; Claude Code's `[Image: source:]`
  line folds into its turn; uploads under `<data dir>/drops/` are listed.
- Update check: a checkout holding commits a newer release lacks reports
  `diverged_from_release` instead of offering a fast-forward that can only fail.

client/src/components/run/ChatFilePreview.tsx

@@ -31,7 +31,9 @@ export interface PreviewScope {
 }
 
 const IMAGE_RE = /\.(png|jpe?g|gif|webp)$/i;
-const DROP_RE = /\/agenthub-drops-\d+\/([0-9a-f]{16}(?:-[A-Za-z0-9._-]+)?\.[A-Za-z0-9]+)$/;
+// The drop dir (`<data dir>/drops/`), or the older `<tmp>/agenthub-drops-<uid>/`.
+const DROP_RE =
+  /\/(?:agenthub-drops-\d+|drops)\/([0-9a-f]{16}(?:-[A-Za-z0-9._-]+)?\.[A-Za-z0-9]+)$/;
 
 export const baseName = (p: string) => p.split("/").pop() || p;
 /** `report.v2.xlsx` → `XLSX`; none → "". */