fix(whatsapp): add free_response_chats, mention stripping, and interactive message unwrapping

Address feature gaps vs Telegram/Discord/Mattermost adapters:
- free_response_chats whitelist to bypass mention gating per-group
- strip bot @phone mentions from body before forwarding to agent
- unwrap templateMessage/buttonsMessage/listMessage in bridge
- info-level log on successful mention pattern compilation
- use module-level json import instead of inline import in config
- eliminate double _normalize_whatsapp_id call via walrus operator
- hoist botIds computation outside per-message loop in bridge

gateway/config.py

@@ -569,8 +569,12 @@ def load_gateway_config() -> GatewayConfig:
                 if "require_mention" in whatsapp_cfg and not os.getenv("WHATSAPP_REQUIRE_MENTION"):
                     os.environ["WHATSAPP_REQUIRE_MENTION"] = str(whatsapp_cfg["require_mention"]).lower()
                 if "mention_patterns" in whatsapp_cfg and not os.getenv("WHATSAPP_MENTION_PATTERNS"):
-                    import json as _json
-                    os.environ["WHATSAPP_MENTION_PATTERNS"] = _json.dumps(whatsapp_cfg["mention_patterns"])
+                    os.environ["WHATSAPP_MENTION_PATTERNS"] = json.dumps(whatsapp_cfg["mention_patterns"])
+                frc = whatsapp_cfg.get("free_response_chats")
+                if frc is not None and not os.getenv("WHATSAPP_FREE_RESPONSE_CHATS"):
+                    if isinstance(frc, list):
+                        frc = ",".join(str(v) for v in frc)
+                    os.environ["WHATSAPP_FREE_RESPONSE_CHATS"] = str(frc)
     except Exception as e:
         logger.warning(
             "Failed to process config.yaml — falling back to .env / gateway.json values. "