feat: implement tier-a4 tts voice output replies

config/default.yaml

@@ -476,6 +476,21 @@ hooks:
 #     timeout_ms: 120000
 #     allow_manual_toggle: true
 
+# ── Text-to-Speech (TTS) Output ──────────────────────────────────────
+# Optional voice output for assistant replies. Uses an OpenAI-compatible
+# /v1/audio/speech endpoint and attaches audio to channel replies.
+#
+# tts:
+#   enabled: false
+#   enabled_channels: [telegram, whatsapp, discord] # Empty = all channels
+#   provider:
+#     type: openai                                  # openai | custom
+#     endpoint: "https://api.openai.com/v1/audio/speech"
+#     api_key: "${OPENAI_API_KEY}"                  # Optional Bearer token
+#     model: "gpt-4o-mini-tts"
+#     voice: "alloy"
+#     format: "mp3"                                 # mp3 | wav | opus
+
 # ── Sub-Agent Configs ────────────────────────────────────────────────
 # Named agent configurations for delegation via agent.delegate tool.
 # Each agent gets a focused system prompt, model tier, and tool profile.