feat(run): show externally started Claude sessions in the active-runs list

The Workspace active-runs list only knew about runs this dashboard spawned,
so two `claude` sessions started by hand in terminal tabs showed up nowhere —
the list read "no active runs" while two agents were working.

Poll GET /api/sessions?status=active alongside the run list and merge those
sessions in as live rows, deduped against dashboard runs by session_id and
filtered to local sources with a cwd (a remote-source or cwd-less session
cannot be resumed on this machine).

External rows get no Attach action: the dashboard owns no tmux session for
them, so there is no PTY to bridge. They offer Resume, which reuses the
existing ensure-lane + start-with-resumeSessionId path to spawn a new
tmux-backed `claude --resume` in that folder — a second process on the same
transcript, not a view of the original terminal.

client/src/i18n/locales/en/run.json

@@ -116,7 +116,9 @@
   "runs": {
     "allSessionsLink": "See all Claude Code sessions →",
     "attached": "Attached to existing run",
-    "scopeNote": "Only shows runs you started from this dashboard.",
+    "externalBadge": "external",
+    "externalHint": "Started outside the dashboard, so there is no terminal to attach to. Resume opens a new tmux-backed `claude --resume` of this session in its folder.",
+    "scopeNote": "Runs started from this dashboard, plus Claude Code sessions running outside it.",
     "started": "Started {{when}}",
     "switcher": "Active runs",
     "switcherEmpty": "No active runs",