fix: cap selfbot stream -maxrate at lib's 10 Mbps ceiling; add stream-test tooling

- selfbot.ts: the @dank074 lib advertises a hardcoded max_bitrate of 10 Mbps to
  Discord (BaseMediaConnection: `max_bitrate: 10000 * 1000`). Our encoder used
  -maxrate = 1.5x target (12 Mbps at 8 Mbps target), so high-motion bursts
  exceeded the negotiated ceiling and WebRTC dropped packets (viewer stutter).
  Cap -maxrate at 10 Mbps.
- Add bot/scripts/stream-test/: env-driven stream-hold.ts (persistent Go-Live
  holder), human.mjs (real xdotool mouse/keyboard + char-by-char typing), and
  scenario.mjs (YouTube/Naver browse). Channel/guild/video are env-parametrised.
- .env.example: document DISCORD_VOICE_CHANNEL_ID for the stream-test scripts.

bot/scripts/stream-test/stream-hold.ts

@@ -0,0 +1,47 @@
+// Persistent selfbot stream holder for manual/operational testing of the
+// Go-Live broadcast. Joins the voice channel, goes live, and keeps the stream
+// up until stopped (SIGTERM/SIGINT) or HOLD_MS elapses. All parameters come
+// from the environment (.env).
+//
+//   bun bot/scripts/stream-test/stream-hold.ts
+//
+// Requires in .env: DISCORD_SELFBOT_TOKEN, DISCORD_GUILD_ID,
+// DISCORD_VOICE_CHANNEL_ID. Stream params: VNC_RESOLUTION, VNC_FRAMERATE,
+// VNC_BITRATE_KBPS, STREAM_HW, VNC_DISPLAY (same vars the bot uses).
+import "dotenv/config";
+import { SelfbotStreamer } from "../../src/stream/selfbot.ts";
+
+const config = {
+  selfbotToken: process.env.DISCORD_SELFBOT_TOKEN ?? "",
+  vncDisplay: process.env.VNC_DISPLAY ?? ":1",
+  vncResolution: process.env.VNC_RESOLUTION ?? "1920x1080",
+  vncFramerate: parseInt(process.env.VNC_FRAMERATE ?? "60", 10),
+  vncBitrateKbps: parseInt(process.env.VNC_BITRATE_KBPS ?? "8000", 10),
+  streamHw: (process.env.STREAM_HW ?? "1") !== "0",
+} as any;
+
+const guildId = process.env.DISCORD_GUILD_ID;
+const voiceChannelId = process.env.DISCORD_VOICE_CHANNEL_ID;
+if (!config.selfbotToken || !guildId || !voiceChannelId) {
+  console.error("Missing DISCORD_SELFBOT_TOKEN / DISCORD_GUILD_ID / DISCORD_VOICE_CHANNEL_ID in .env");
+  process.exit(1);
+}
+
+const s = new SelfbotStreamer(config);
+const maxMs = parseInt(process.env.HOLD_MS ?? "7200000", 10);
+let stopped = false;
+const stop = async () => {
+  if (stopped) return;
+  stopped = true;
+  console.log("STREAM_STOPPING");
+  await s.stop();
+  console.log("STREAM_STOPPED");
+  process.exit(0);
+};
+process.on("SIGTERM", stop);
+process.on("SIGINT", stop);
+
+const r = await s.start({ guildId, voiceChannelId } as any);
+console.log(`STREAM_START: ${r} active:${s.isActive()} (${config.vncResolution}@${config.vncFramerate} ${config.vncBitrateKbps}k hw=${config.streamHw})`);
+setTimeout(stop, maxMs);
+setInterval(() => {}, 60000);