refactor: 引擎源码移至 src/，编译产物统一至 release/

- 源码: engines/c/ → engines/src/c/
- 源码: engines/cpp/ → engines/src/cpp/
- 源码: engines/fortran/ → engines/src/fortran/
- 编译产物: engines/release/ (静态编译)
  - dynamics_c.exe   (516KB, C 引擎)
  - dynamics_cpp.exe (3.3MB, C++ 引擎)
  - dynamics_f90.exe (988KB, Fortran 引擎)
- compute.py: engine_map 指向 release/
- compute.py: param.json 和校准缓存移至 release/
- engine_dll.py: DLL 搜索路径指向 release/
- release/ 目录纳入 git 版本管理，用户克隆后直接可用

compute.py

@@ -1134,11 +1134,11 @@ def run_engine(engine, input_dir, output_dir, config):
     script_dir = os.path.dirname(os.path.abspath(__file__))
     system = platform.system().lower()
     engine_map = {
-        "c":       "engines/c/build/dynamics_c",
-        "cpp":     "engines/cpp/build/dynamics_cpp",
-        "c++":     "engines/cpp/build/dynamics_cpp",
-        "fortran": "engines/fortran/build/dynamics_f90",
-        "f90":     "engines/fortran/build/dynamics_f90",
+        "c":       "engines/release/dynamics_c",
+        "cpp":     "engines/release/dynamics_cpp",
+        "c++":     "engines/release/dynamics_cpp",
+        "fortran": "engines/release/dynamics_f90",
+        "f90":     "engines/release/dynamics_f90",
         "python":  None,  # 特殊处理：用 sys.executable 调用 main.py
     }
     if engine not in engine_map:
@@ -1208,7 +1208,7 @@ def run_engine(engine, input_dir, output_dir, config):
         "camera_center_y": float(config.get("camera_center_y", 0.0)),
         "camera_center_z": float(config.get("camera_center_z", 0.0)),
     }
-    param_path = os.path.join(script_dir, "engines", engine, "param.json")
+    param_path = os.path.join(script_dir, "engines", "release", f"{engine}.json")
     os.makedirs(os.path.dirname(param_path), exist_ok=True)
     with open(param_path, "w", encoding="utf-8") as f:
         json.dump(param_json, f, indent=2)
@@ -1226,7 +1226,7 @@ def run_engine(engine, input_dir, output_dir, config):
     n_atoms_calib = len(ATOM_IDS) if ATOM_IDS is not None else 0
 
     # 尝试读取缓存；当 n_atoms 相同且 NT 在 50% 范围内时视为有效
-    _cache_path = os.path.join(script_dir, "engines", engine, "_calib_cache.json")
+    _cache_path = os.path.join(script_dir, "engines", "release", f"_calib_{engine}.json")
     _step_time = None
     try:
         with open(_cache_path, encoding="utf-8") as _cf:
@@ -1241,10 +1241,10 @@ def run_engine(engine, input_dir, output_dir, config):
     if _step_time is None:
         _calib_param = dict(param_json)
         _calib_param["NT"] = _calib_nt
-        _calib_path = os.path.join(script_dir, "engines", engine, "_calib.json")
+        _calib_path = os.path.join(script_dir, "engines", "release", f"_calib_{engine}.json")
         with open(_calib_path, "w", encoding="utf-8") as _cf:
             json.dump(_calib_param, _cf, indent=2)
-        _calib_outdir = os.path.join(script_dir, "engines", engine, "_calib_out")
+        _calib_outdir = os.path.join(script_dir, "engines", "release", f"_calib_{engine}_out")
         os.makedirs(_calib_outdir, exist_ok=True)
         _ct0 = time.time()
         subprocess.run(