docs(bot-mode): explain Warm Bot Backends, idle reaping, and slot waits

Fleet users read "Hermes backend for profile X exited (1)" as a crash and
raise Warm Bot Backends past their profile count to make it stop. Name the
setting, the defaults, what the exit line means, and which operations take
a slot so the knob is tuned for active bots instead of total profiles.

website/docs/user-guide/bot-mode.md

@@ -255,6 +255,12 @@ Clicking a Connections Bot does **not** hop your window onto that machine — st
 
 See [Connecting Desktop to Many Hermes Instances](./multi-connection-desktop.md) for the full multi-connection guide.
 
+## Warm Bot Backends (how many bots run at once)
+
+Each local Bot runs in its own backend process, and Desktop keeps at most **Settings → Advanced → Warm Bot Backends** of them alive at once (default 3, ~60 MB each). Idle backends are reaped after the idle timeout next to that setting (default 10 minutes); the `Hermes backend for profile "<name>" exited (1)` line in `desktop.log` that follows an idle-reap message is that cleanup, not a crash. A Bot you open while every slot is busy waits up to 30 seconds for a slot, then fails with *timed out waiting for a free local slot*.
+
+Reads of another Bot's chat history and background transcript refreshes do **not** take a slot — only an interactive open or a running turn does. If you drive a large fleet (group chats with many members, or Kanban dispatch across many profiles), raise Warm Bot Backends toward the number of Bots you expect to be active at the same time and give the machine the memory to match. Setting it higher than the profiles you actually use only adds startup work.
+
 ## Turning it off
 
 Bot Mode is a bundled desktop plugin. Flip its **Desktop** switch off in **Capabilities → Plugins → Bots** — the roster, the Routines pane, and the composer middleware unregister live, no restart needed. Your profiles, sessions, and cron jobs are untouched either way; Bot Mode never owns your data, it only renders it.