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.

server/routes/sessions.js

@@ -379,9 +379,10 @@ const outlineEvents = db.prepare(
 );
 // A file the composer attached (`/api/run/drop-*` names it), as its path is
 // pasted into the prompt; and a Claude Code memory file.
+// The drop dir is `<data dir>/drops/`; older transcripts name `<tmp>/agenthub-drops-<uid>/`.
 const UPLOAD_RE =
-  /(?:^|\s)(\S*\/agenthub-drops-\d+\/[0-9a-f]{16}(?:-[A-Za-z0-9._-]+)?\.[A-Za-z0-9]+)/g;
-const isUpload = (p) => /\/agenthub-drops-\d+\//.test(p);
+  /(?:^|\s)(\S*\/(?:agenthub-drops-\d+|drops)\/[0-9a-f]{16}(?:-[A-Za-z0-9._-]+)?\.[A-Za-z0-9]+)/g;
+const isUpload = (p) => /\/(?:agenthub-drops-\d+|drops)\/[0-9a-f]{16}/.test(p);
 const isMemory = (p) => /\/\.claude\/.*\/memory\//.test(p);
 /** Records `p` once, newest last. */
 const touch = (set, p) => {