Let a user stop a bot, and say the app is still alpha

The thinking row and the header menu both carry Stop while a bot has work
open for the user anywhere: every pending or processing job of that bot in
their conversations is failed as stopped, its task closed, a Stopped step
recorded and one closing message posted per session, so the thread stops
waiting and the bot goes idle. The handler running the job is aborted from
this process through a registry, so a job stuck waiting on a model stops at
once instead of on its next heartbeat, and a late face change after the
abort is dropped.

The release stage is now said in the app too: Settings > General reports
"Cobble v0.1.5 (alpha)" next to development, and the README and RELEASING.md
say what alpha means for installs.

src/pages/admin/bots/[bot_id]/(partials)/conversation-header-menu.tsx

@@ -16,6 +16,7 @@ import BotRoutinesModal from "./bot-routines-modal";
 import BotModelsModal from "./bot-models-modal";
 import HeaderMenuItem from "./header-menu-item";
 import NewSessionButton from "./new-session-button";
+import StopBotButton from "./stop-bot-button";
 
 type Props = {
     bot: BotWithLastMessage;
@@ -48,8 +49,9 @@ type Props = {
 
 /**
  * The conversation header's menu: the sessions, a new session, the bot's
- * computer, its models and its settings. A row that opens a modal closes
- * the menu first, so the modal never sits behind an open menu.
+ * computer, its models, its settings and, while it works, stopping it. A
+ * row that opens a modal closes the menu first, so the modal never sits
+ * behind an open menu.
  */
 export default function ConversationHeaderMenu({
     bot,
@@ -136,6 +138,8 @@ export default function ConversationHeaderMenu({
                     onSaved={on_model_saved}
                 />
             </Stack>
+            <Divider className="my-1 mx-3 w-auto border-hairline dark:border-hairline" />
+            <StopBotButton menu bot_name={bot.name} />
             {can_open_settings ? (
                 <>
                     <Divider className="my-1 mx-3 w-auto border-hairline dark:border-hairline" />