feat: v2.7.8 — Artifacts hub, clone related repos as extra folders, quieter resume prompt

- Artifacts (/artifacts): claude.ai pages sessions publish (captured from the
  Artifact tool's hook), pinned workspace files, skills and plugins, each
  kept as a snapshot; shared ones appear in a Hub and a skill or plugin
  installs into the viewer's own account (server/lib/artifacts.js,
  /api/artifacts, docs/plans/artifacts/).
- Workspace extra folders: clone one or more related repos beside the
  workspace and add them in one step (POST /api/lanes/:id/sources/clone).
- A pane that ended by itself while tmux kept running is no longer offered
  for resume (tmux.serverStartedAt in reconcileOrphans).
- Changes panel: a folder that is not a git repo opens on Files, and its
  files open from there.
- Plus the parallel sessions' work in this tree: File Explorer button in the
  panel header, user delete, RSA SSH keys, chat/terminal and pet fixes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/lib/tmux.js

@@ -386,6 +386,22 @@ function serverPid() {
   }
 }
 
+/**
+ * When the tmux server that holds (or held) session `name` started, in epoch
+ * ms — the host's, or the member's under S3 — or null when there is no such
+ * server or it cannot be asked. A pane gone while its server ran on since
+ * before the pane began exited by itself; one whose server is gone or newer
+ * died with it (a reboot, a killed tmux).
+ */
+function serverStartedAt(name) {
+  try {
+    const out = String(onServerOf(name, ["display-message", "-p", "#{start_time}"])).trim();
+    return /^\d+$/.test(out) ? Number(out) * 1000 : null;
+  } catch {
+    return null;
+  }
+}
+
 /** `-e NAME=value` pairs for tmux, in a stable order. */
 function envFlags(env) {
   const flags = [];
@@ -703,6 +719,7 @@ module.exports = {
   capturePane,
   sendKey,
   killSession,
+  serverStartedAt,
   listSessions,
   liveSessions,
   isTmuxAvailable,