fix(bot): never broadcast on the conversation's account (it deafened STT)

Critical regression: in single-account userbot mode the broadcast auto-start
logged in a SECOND session of the conversation account and called joinVoice,
which the streaming lib always sends with self_deaf:true. Voice state is
per-account, so this deafened the CONVERSATION session too and the bot silently
stopped hearing the user (STT receive broke). The Go-Live cannot connect on a
shared account anyway.

start() now refuses early (no joinVoice, no deafen) when there is no dedicated
DISCORD_STREAM_TOKEN and no normal-bot token, protecting the conversation. A
dedicated stream account re-enables the broadcast.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

bot/src/stream/selfbot.test.ts

@@ -46,6 +46,8 @@ test("a self-ended stream tears down the capture pipeline (no ffmpeg leak)", asy
   const { SelfbotStreamer } = await import("./selfbot.ts");
   const s = new SelfbotStreamer({
     selfbotToken: "token",
+    streamToken: "stream-token", // dedicated broadcast account -> broadcast allowed
+    botToken: "",
     vncDisplay: ":1",
     vncResolution: "1920x1080",
     vncFramerate: 60,
@@ -104,6 +106,8 @@ test("a Go-Live that never connects is reported as failed, not live, and is torn
   const { SelfbotStreamer } = await import("./selfbot.ts");
   const s = new SelfbotStreamer({
     selfbotToken: "token",
+    streamToken: "stream-token", // dedicated broadcast account -> broadcast allowed
+    botToken: "",
     vncDisplay: ":1",
     vncResolution: "1920x1080",
     vncFramerate: 60,