feat(libmsg): add pymsg C++ library with AsyncQueue, MsgServer, and JSON RPC layer

- Add libmsg module: pymsg protocol implementation (4-byte BE length prefix + UTF-8)
- Add AsyncQueue<T>: generic async batch queue with backpressure (aligned with Python AsyncRpcQueue)
- Add MsgServer: select-based multi-client TCP server with optional thread pool
- Add RpcClient/RpcServer: JSON RPC convention layer with automatic route injection
- Refactor gateway/LogC.hpp to use AsyncQueue for async batch log delivery
- Update gateway/DbC.hpp to add call_msg() using pymsg TCP protocol
- Remove duplicated gateway/inc/Msg.hpp (now provided by libmsg)
- Update gateway/Makefile and _inst.sh build order

Fixes included:
- pmsg_send size check uses kMaxMsgSize (64MiB) instead of 4GiB
- MsgClient._running uses std::atomic<bool> for thread safety
- Deadline-based recv timeout to prevent Slowloris (header+payload shared deadline)

gateway/Makefile

@@ -1,10 +1,10 @@
-VERSION := 0.0.1
+VERSION := 0.8.0
 APP_NAME := gateway
 INSTL_DIR := /usr/local/bin
 CPP := g++
-INCS := -I inc/
-MY_LIBS := -L/usr/lib -lus_http -lus_httpclient -lus_crypt
-LIBS := -pthread -lcurl -lssl -lsqlite3 -lz -lcrypto -lboost_json -lboost_program_options
+INCS := -I inc/ -I ../libmsg/inc
+MY_LIBS := -L/usr/lib -L../libmsg/build -lus_http -lus_httpclient -lus_crypt -lus_msg
+LIBS := -pthread -lcurl -lssl -lsqlite3 -lz -lcrypto -lboost_json -lboost_program_options -Wl,-rpath,$(shell cd ../libmsg/build && pwd)
 CPPFLAGS := --std=c++20 -pipe -pthread # -Wall -Werror
 BUILD_DIR = build
 $(shell mkdir -p $(BUILD_DIR))
@@ -13,7 +13,7 @@ $(shell mkdir -p $(BUILD_DIR))
 all: $(BUILD_DIR)/$(APP_NAME).out
 $(BUILD_DIR)/$(APP_NAME).out:	$(BUILD_DIR)/main.o
 	$(CPP) $^ $(LIBS) $(MY_LIBS) -o $@
-$(BUILD_DIR)/main.o:	src/main.cpp
-	$(CPP) $(CPPFLAGS) -c $^ $(INCS) -o $@
+$(BUILD_DIR)/main.o:	src/main.cpp inc/DbC.hpp inc/LogC.hpp inc/Conf.hpp inc/ExpBase.hpp inc/LocalTime.hpp
+	$(CPP) $(CPPFLAGS) -c $< $(INCS) -o $@
 clear:
 	@rm -rvf build/