Subagents: a new chat reads /models again, so subagents switched on later show

The Subagents chip on a new chat follows `/models` -> model.subagents.offered, the same
team_run.offered the web page renders from. The app read /models once, at sign-in, and kept
it while it stayed open in the tray: subagents switched on afterwards (or a model added)
never reached a new chat until a restart. startNew() now re-reads it (at most every 5 s,
keeping the last list if the read fails) and redraws the draft's chips (modelsChanged()).
An open chat already re-reads its own `subagents` with GET /chats/{id}.

tests/ui: A5 cases -- parallel model offered: chip, slider to the server's cap, no note;
one-request model offered named_only: the `own` note; offered false everywhere: no chip;
switched on while open: the next new chat has it; an open chat follows its `subagents`.

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

CHANGELOG.md

@@ -16,6 +16,11 @@ All notable changes to LLeMbas Desktop. The format follows
   subagent asks when one does. A card already on the screen is kept as it is while the reply goes
   on, so a command being corrected or an option picked is no longer lost when the server sends
   the list again; a card that cannot be drawn says why instead of leaving an empty space.
+- **Subagents after they are switched on.** The app read which models a new chat is offered
+  subagents on only when it signed in, so subagents switched on (or a model added) on the server
+  while the app stayed open in the tray never showed on a new chat until it was restarted. A new
+  chat now asks the server again. (An agent chat has no Subagents setting: its subagents run on
+  the computer, and the server offers none for it.)
 
 ### Added