refactor: 移除旧子进程模式的 main.* 源文件，Makefile 只编译 DLL

- 删除 engines/c/main.c, engines/cpp/main.cpp, engines/fortran/main.f90
- Makefile 移除 all/exe 构建目标，默认只编译 DLL

engines/c/Makefile

@@ -1,21 +1,17 @@
 # engines/c/Makefile
-# 跨平台编译：make         → 本地系统编译
-#              make linux  → Linux 交叉编译（需 x86_64-linux-gnu-gcc）
+# 编译 DLL（主程序通过 ctypes 直接调用）
+#              make dll     → 本地系统编译
+#              make linux   → Linux 交叉编译（需 x86_64-linux-gnu-gcc）
 #              make windows → Windows 交叉编译（需 x86_64-w64-mingw32-gcc）
-#              make macos  → macOS 交叉编译（需 osxcross 工具链）
 
 CC        = gcc
 CFLAGS    = -O3 -march=native -Wall -Wextra
 LDFLAGS   = -lm
-SRCS      = main.c
 LIB_SRC   = dynamics_lib.c
 
 # 自动检测系统
 UNAME_S  := $(shell uname -s 2>/dev/null || echo Windows)
 
-# 目标文件名：统一使用 .exe 后缀（方便 Python 跨平台调用）
-TARGET    = build/dynamics_c.exe
-
 # DLL 目标（平台自动选择后缀）
 ifeq ($(UNAME_S),Linux)
   DLL_TARGET = build/dynamics_c.so
@@ -28,17 +24,12 @@ else
   DLL_FLAGS  = -shared
 endif
 
-# ── 本地编译 ─────────────────────────────────
-.PHONY: all dll clean linux windows macos
+.PHONY: all dll clean
 
-all: $(TARGET)
+all: dll
 
 dll: $(DLL_TARGET)
 
-$(TARGET): $(SRCS) | build
-	$(CC) $(CFLAGS) -o $@ $(SRCS) $(LDFLAGS)
-	@echo "  === C engine built: $@ ==="
-
 $(DLL_TARGET): $(LIB_SRC) | build
 	$(CC) $(CFLAGS) $(DLL_FLAGS) -o $@ $(LIB_SRC) $(LDFLAGS)
 	@echo "  === C DLL built: $@ ==="
@@ -46,37 +37,5 @@ $(DLL_TARGET): $(LIB_SRC) | build
 build:
 	mkdir -p build
 
-# ── 交叉编译 ─────────────────────────────────
-# Linux → Linux (x86_64)
-linux: CROSS_PREFIX = x86_64-linux-gnu-
-linux: CC = $(CROSS_PREFIX)gcc
-linux: CFLAGS = -O3 -march=x86-64 -Wall -Wextra
-linux: $(SRCS) | build
-	$(CC) $(CFLAGS) -o build/dynamics_c_linux.exe $(SRCS) $(LDFLAGS)
-	@echo "  === Linux binary: build/dynamics_c_linux.exe ==="
-
-# 任意平台 → Windows (x86_64)
-# 需要安装 MinGW 交叉编译器：
-#   apt install mingw-w64 (Debian/Ubuntu)
-#   brew install mingw-w64 (macOS)
-windows: CROSS_PREFIX = x86_64-w64-mingw32-
-windows: CC = $(CROSS_PREFIX)gcc
-windows: CFLAGS = -O3 -march=x86-64 -Wall -Wextra
-windows: $(SRCS) | build
-	$(CC) $(CFLAGS) -o build/dynamics_c_win.exe $(SRCS) $(LDFLAGS)
-	@echo "  === Windows binary: build/dynamics_c_win.exe ==="
-
-# 任意平台 → macOS (x86_64)
-# 需要安装 osxcross 工具链
-macos: CROSS_PREFIX = x86_64-apple-darwin-
-macos: CC = $(CROSS_PREFIX)gcc
-macos: CFLAGS = -O3 -march=x86-64 -Wall -Wextra
-macos: $(SRCS) | build
-	$(CC) $(CFLAGS) -o build/dynamics_c_mac.exe $(SRCS) $(LDFLAGS)
-	@echo "  === macOS binary: build/dynamics_c_mac.exe ==="
-
-# ── 编译所有平台 ──────────────────────────────
-all-platforms: linux windows macos
-
 clean:
 	rm -rf build *.o