Chat tabs, chat mode, own modes, compaction notice, CLI binaries again

- Terminals and file managers as tabs of a chat; chat terminals keep running on
  the server (no idle timeout) and re-attach from any device
- "Just chat" in New session and a built-in chat mode with a lean prompt and only
  web tools; custom modes with kind (coding/conversation), read-only and tool picker
- Mode selector as a dropdown
- The chat shows running compactions (automatic: tokens and share of the limit)
  and labels summaries
- Docker image builds and serves the terminal client binaries again
- Fix: atomic session updates; background title/usage writes no longer undo each
  other (auto compaction triggered one turn late)

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

web/src/components/Composer.tsx

@@ -288,20 +288,20 @@ export function Composer({
         />
         <div className="composer-bar">
           <div className="composer-options">
-          <div className="mode-tabs" role="tablist" aria-label={t("composer.mode")}>
+          <select
+            className="mode-select"
+            value={session.agent}
+            onChange={(e) => onUpdate({ agent: e.target.value })}
+            aria-label={t("composer.mode")}
+            title={agents.find((a) => a.name === session.agent)?.description ?? t("composer.mode")}
+          >
+            {!agents.some((a) => a.name === session.agent) && <option value={session.agent}>{session.agent}</option>}
             {agents.map((a) => (
-              <button
-                key={a.name}
-                role="tab"
-                aria-selected={session.agent === a.name}
-                className={session.agent === a.name ? "active" : ""}
-                title={a.description}
-                onClick={() => onUpdate({ agent: a.name })}
-              >
+              <option key={a.name} value={a.name} title={a.description}>
                 {a.name}
-              </button>
+              </option>
             ))}
-          </div>
+          </select>
           {session.agent === "craft" && (
             <div className="mode-tabs" role="tablist" aria-label={t("craft.mode")} title={t("craft.modeHint")}>
               <button className={session.clean_room !== false ? "active" : ""} onClick={() => onUpdate({ clean_room: true })}>