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/dict/bot-queue-dict.ts

@@ -4,6 +4,30 @@
  */
 export const BotJobCancelledError = "Cancelled";
 
+/**
+ * `last_error` of a job the user stopped from the chat. A stopped job is
+ * never retried and never told about: the user pulled the plug.
+ */
+export const BotJobStoppedError = "Stopped by the user";
+
+/**
+ * The last step recorded on a stopped job. It's a step, not a message, so a
+ * bot that was stopped mid-thought doesn't answer on its own.
+ */
+export const BotJobStoppedStep = "Stopped";
+
+/**
+ * What the thinking row's stop button says, so the row and its tooltip
+ * never drift.
+ */
+export const BotStopButtonLabel = "Stop";
+
+/**
+ * What the bot says in the conversation once the user has stopped it. It's
+ * the bot's turn again, so the thread stops waiting on a reply.
+ */
+export const BotStoppedMessage = "Stopped. I'll carry on when you ask me to.";
+
 /**
  * `last_error` bun-sqlite sets when it releases a job whose handler went
  * silent past the lock timeout on its last attempt.