feat: add Mixture of Agents (MoA) for arbiter verdicts

When MOA_ENABLED=true, arbiter queries multiple LLM models in parallel
via OpenAI-compatible API, then an aggregator model synthesizes the
final verdict from all opinions. Falls back to single-agent arbiter
when MoA is disabled.

Config: MOA_BASE_URL, MOA_API_KEY, MOA_REFERENCE_MODELS, MOA_AGGREGATOR_MODEL

.env.example

@@ -57,6 +57,15 @@ STATUS_CHANNEL_ID=                    # Discord channel ID for live status updat
 # ARBITER_EFFORT=high                   # Arbiter effort override
 # ARBITER_FALLBACK_ENABLED=true         # Fall back to codex on Claude failure (default: true)
 
+# --- Mixture of Agents (MoA) ---
+# Queries multiple models in parallel for arbiter verdicts, then aggregates.
+# Requires OpenAI-compatible API (OpenRouter recommended for multi-model access).
+# MOA_ENABLED=true
+# MOA_BASE_URL=https://openrouter.ai/api/v1
+# MOA_API_KEY=sk-or-xxx
+# MOA_REFERENCE_MODELS=anthropic/claude-sonnet-4-6,openai/gpt-5.4,deepseek/deepseek-chat
+# MOA_AGGREGATOR_MODEL=anthropic/claude-opus-4-6
+
 # --- Advanced ---
 # MAX_CONCURRENT_AGENTS=5             # Max parallel agent processes
 # SESSION_COMMAND_ALLOWED_SENDERS=    # Comma-separated Discord user IDs for session commands