docs: 更新 examples 文档，移动引擎源码结构

- 更新 examples/Readme.md 覆盖全部 10 个案例
- 新增 examples/Readme.html 案例总览页面
- 引擎源码移至 engines/src/ 目录
- 编译产物统一至 engines/release/（静态编译）
- compute.py/engine_dll.py 路径同步更新

engines/release/c.json

@@ -1,8 +1,8 @@
 {
   "box_a": 300.0,
-  "NT": 1000000,
+  "NT": 10000,
   "DT": 0.001,
-  "NSTEP": 500,
+  "NSTEP": 20,
   "warmup_steps": 0,
   "method": "leapfrog",
   "G": [
@@ -11,14 +11,14 @@
     0.0
   ],
   "B": [
-    0.01,
+    0.005,
     0.0,
-    0.01
+    0.005
   ],
   "gravity_field": 0,
   "gravity_interaction": 0,
   "elastic_force": 1,
-  "damping_force": 1,
+  "damping_force": 0,
   "gravity_strength": 1.0,
   "driving_force": 1,
   "save_trajectory": 0,