feat(bot+dashboard): bot info, server/voice-channel picker, participants, speaker

Adds a dashboard<->bot control plane (bot pushes state + polls commands, keeping
the bot's single outbound-HTTP direction):
- New bot_control.BotControl + endpoints: GET /api/bot/state, /api/bot/commands;
  POST /api/bot/report, /api/bot/select.
- Dashboard header bar: bot identity/connection, server dropdown (top "없음"),
  voice-channel dropdown (top "없음"), and live participant list.
- Turns record who spoke (Turn.speaker, via X-User-Name on the voice-turn POST).
- dave/bot.mjs: reports identity/guilds/voice-channels/members, polls join/leave
  commands and joins dynamically, and sends the speaker's display name.

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

wsai/monitor.py

@@ -80,6 +80,7 @@ class Turn:
         self._monitor = monitor
         self.id = turn_id
         self.source = source
+        self.speaker = ""  # who spoke (Discord display name), when known
         self.wall = _now_wall()
         self._t0 = _now_mono()
         self.heard_text = ""
@@ -137,6 +138,7 @@ class Turn:
         return {
             "id": self.id,
             "source": self.source,
+            "speaker": self.speaker,
             "wall": self.wall,
             "heard": self.heard_text,
             "thought": self.thought_text,