Subagents by name; the activity panel as the reference: header button, compact, tasks

- "Subagents" everywhere a person reads it (chip, popover with Fewest/Most, scheduled task,
  panel); offered per the server's `subagents` on a model or chat where it says it, else as
  before; the fields' most is the server's cap, else 32. No subagent-model setting.
- Panel: always reachable from the header's button; the line above the composer only while
  something runs; Environment for an agent chat; Context with "N until auto-compact" and a
  Compact button (POST /chats/{chat}/compact; a server without it is said so); Background
  tasks under Running with elapsed time and a stop square each, unfolding to kind, step,
  live text and conversation, nested tasks folded under their parent, Finished N folded;
  Room and Plan as sections.
- i18n: 24 new sentences x 8 languages, 9 retired; CHANGELOG [Unreleased].

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

ui/js/dom.js

@@ -81,6 +81,7 @@ export const ICONS = {
   attach: "M7.25 2.5h1.5v4.75h4.75v1.5H8.75v4.75h-1.5V8.75H2.5v-1.5h4.75z",
   bolt: "M9.5 1L3 9.25h4.25L6.5 15 13 6.75H8.75z",
   stop: "M4.5 4.5h7v7h-7z",
+  tasks: "M2 3.25h2v2H2zM5.5 3.5H14V5H5.5zM2 7h2v2H2zM5.5 7.25H14v1.5H5.5zM2 10.75h2v2H2zM5.5 11H14v1.5H5.5z",
   back: "M10 3.5L5.5 8 10 12.5 11.1 11.4 7.7 8 11.1 4.6z",
   terminal: "M1.5 2.5h13v11h-13zM3 4v8h10V4zM4.2 5.4l2.6 2.6-2.6 2.6-1-1L4.8 8 3.2 6.4zM7.5 10h4v1.5h-4z",
   search: "M7 2a5 5 0 013.95 8.07l3.24 3.24-1.06 1.06-3.24-3.24A5 5 0 117 2zm0 1.5a3.5 3.5 0 100 7 3.5 3.5 0 000-7z",