feat(selfbot): dedicated DISCORD_STREAM_TOKEN for the broadcast account

Confirmed root cause of "broadcast doesn't appear in Discord" in userbot mode:
the conversation and the Go-Live broadcaster were the SAME Discord account on
two sessions. Discord allows one voice presence per account, so the broadcaster's
voice connection never connects (state voiceReady:false). Proven by isolating the
broadcaster: alone it connects ("Go-Live WebRTC connected"); alongside the
conversation it times out.

The broadcaster now logs in with DISCORD_STREAM_TOKEN when set (a second burner
account dedicated to streaming), falling back to DISCORD_SELFBOT_TOKEN (correct
for normal-bot mode). When userbot mode shares one account it warns loudly with
the fix. Documents the var in .env.example.

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

.env.example

@@ -123,6 +123,14 @@ VNC_BITRATE_KBPS=8000
 # A THROWAWAY/burner Discord user account token. NEVER your main account.
 # Using a selfbot violates Discord ToS and can get the account banned.
 DISCORD_SELFBOT_TOKEN=
+# Dedicated burner account for the Go-Live BROADCAST, separate from the
+# conversation account above. REQUIRED in userbot mode for the broadcast to
+# work: Discord allows only one voice presence per account, so the conversation
+# and the broadcast cannot share one account (the broadcaster's voice connection
+# never connects). Leave empty in normal-bot mode (the conversation runs on the
+# bot account, so the selfbot account is already broadcast-only). Both burner
+# accounts must be in the server. Use a second throwaway account, never a main.
+DISCORD_STREAM_TOKEN=
 # Hardware (NVENC) encode for the stream. 1 = use the GPU (recommended for
 # 1080p60), 0 = software x264. Requires an NVIDIA GPU + ffmpeg built with nvenc.
 STREAM_HW=1