fix: use emoji allowlist instead of length check in pick_reaction

Prevents text words like "skull" from passing the filter and causing
Discord HTTPException noise.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

utils/llm_client.py

@@ -743,6 +743,12 @@ class LLMClient:
                 self._log_llm("classify_intent", elapsed, False, message_text[:200], error=str(e))
                 return "chat"
 
+    _REACTION_EMOJIS = {
+        "\U0001f480", "\U0001f602", "\U0001f440", "\U0001f525",
+        "\U0001f4af", "\U0001f62d", "\U0001f921", "\u2764\ufe0f",
+        "\U0001fae1", "\U0001f913", "\U0001f974", "\U0001f3af",
+    }
+
     async def pick_reaction(self, message_text: str, channel_name: str) -> str | None:
         """Pick a contextual emoji reaction for a Discord message.
 
@@ -785,7 +791,7 @@ class LLMClient:
                 raw = (response.choices[0].message.content or "").strip()
                 token = raw.split()[0] if raw.split() else ""
 
-                if not token or token.lower() == "none" or len(token) > 7:
+                if not token or token.lower() == "none" or token not in self._REACTION_EMOJIS:
                     self._log_llm("pick_reaction", elapsed, True, message_text[:200], "NONE")
                     return None