feat(dashboard): conversation log filter by time/user/server/channel/content

Adds the requested multi-dimension log search. Turns now carry speaker, guild
and channel (the bot sends X-User/Guild/Channel-Name on the voice-turn POST), and
a filter bar above the conversation feed narrows by 시간(최근 N분)·유저·서버·
채널·내용. The event/error panel keeps its text+level search.

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

dave/bot.mjs

@@ -123,9 +123,15 @@ async function handleUtterance(userId, pcm) {
   } catch {}
   let resp;
   try {
+    const guildName = (currentGuildId && client.guilds.cache.get(currentGuildId)?.name) || '';
     resp = await fetch(VOICE_ENDPOINT, {
       method: 'POST',
-      headers: { 'Content-Type': 'audio/wav', 'X-User-Name': encodeURIComponent(speaker) },
+      headers: {
+        'Content-Type': 'audio/wav',
+        'X-User-Name': encodeURIComponent(speaker),
+        'X-Guild-Name': encodeURIComponent(guildName),
+        'X-Channel-Name': encodeURIComponent(currentChannelName || ''),
+      },
       body: wav,
     });
   } catch (e) {