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/lib/types.ts

@@ -1344,6 +1344,7 @@ export interface UpdateStatusPayload {
   situation?:
     | "plugin_managed"
     | "release_available"
+    | "diverged_from_release"
     | "tracking_canonical"
     | "fork_or_diverged_tracking"
     | "feature_branch"