feat: P04肩叉J1连接处圆盘鼓楞去除，接缝区与P03止脱环齐径齐高，同步重建模型数据与查看器

- 删除 disc_j1(J1 从动法兰圆盘)：盘面在 column 前缘形成鼓楞，J1 连接由
  boss(Ø35.6 贯通 P03 前盖中心孔)直连电机输出盘承担，螺钉走 boss 端面孔
- column 顶边降至 Z=646.5、宽度收至 Y±36.5，与 P03 前置止脱环齐平齐径
- M2 前后端安装件保持原状
- 13/13 构件单实体拓扑通过，8 组接触面碰撞零干涉

docs/bom.json

@@ -4,8 +4,8 @@
   "名称": "立柱下段",
   "类型": "3D打印",
   "数量": 1,
-  "体积cm3": 403.2,
-  "质量g_PLA": 499.9,
+  "体积cm3": 402.4,
+  "质量g_PLA": 499.0,
   "包络": "[-148.0 95.0 10.0 .. -82.0 161.0 188.0] (66.0x66.0x178.0)",
   "说明": "200mm适配分段A：高166mm+16mm阶梯公榫+非对称M4防反装通孔+底部50x50x12榫头+P01-A 竖排TOP刻字"
  },
@@ -14,8 +14,8 @@
   "名称": "立柱中段",
   "类型": "3D打印",
   "数量": 1,
-  "体积cm3": 354.6,
-  "质量g_PLA": 439.8,
+  "体积cm3": 353.9,
+  "质量g_PLA": 438.9,
   "包络": "[-148.0 95.0 172.0 .. -82.0 161.0 337.0] (66.0x66.0x165.0)",
   "说明": "200mm适配分段B：高165mm+双端公母榫+非对称M4防反装通孔+P01-B 竖排TOP刻字"
  },
@@ -24,7 +24,7 @@
   "名称": "立柱上段",
   "类型": "3D打印",
   "数量": 1,
-  "体积cm3": 305.2,
+  "体积cm3": 305.3,
   "质量g_PLA": 378.5,
   "包络": "[-148.0 95.0 321.0 .. -82.0 161.0 470.0] (66.0x66.0x149.0)",
   "说明": "200mm适配分段C：高149mm+底端母榫+非对称M4防反装通孔+顶面P03安装台+P01-C 竖排TOP刻字"
@@ -74,10 +74,10 @@
   "名称": "肩叉",
   "类型": "3D打印",
   "数量": 1,
-  "体积cm3": 357.2,
-  "质量g_PLA": 442.9,
-  "包络": "[-16.5 90.0 455.0 .. 53.5 166.0 648.0] (70.0x76.0x193.0)",
-  "说明": "加长避让版：头部与身子前移加长至X=10.5，与P03锁紧法兰保持2.0mm轴向安全间隙（不做前移，保持输出端最短悬伸力臂），J1输出凸台贯通直连电机，顶部顺滑齐平于Z=648mm，单实体全角度零干涉"
+  "体积cm3": 346.5,
+  "质量g_PLA": 429.7,
+  "包络": "[-16.5 91.5 455.0 .. 53.5 164.5 646.5] (70.0x73.0x191.5)",
+  "说明": "加长避让版：头部与身子前移加长至X=10.5，与P03锁紧法兰保持2.0mm轴向安全间隙（不做前移，保持输出端最短悬伸力臂），J1输出凸台贯通直连电机，J1从动法兰圆盘鼓楞已删（接缝区与P03止脱环齐径齐高R36.5/顶646.5），单实体全角度零干涉"
  },
  {
   "件号": "P05_大臂旋转座",
@@ -104,10 +104,10 @@
   "名称": "小臂骨架",
   "类型": "3D打印",
   "数量": 1,
-  "体积cm3": 208.5,
-  "质量g_PLA": 258.6,
-  "包络": "[-19.4 92.0 187.0 .. 56.4 174.0 369.9] (75.8x82.0x182.9)",
-  "说明": "V2 L型结构：+Y侧背脊立柱避让大臂骨架，过渡区采用与顶面和立柱双相切的R=28mm平滑内凹大圆弧，彻底消除直斜线折角与悬空阶梯小块，下方M5电机半包散热，俯仰大范围自由运动零干涉"
+  "体积cm3": 209.6,
+  "质量g_PLA": 259.9,
+  "包络": "[-16.5 92.0 187.0 .. 53.5 174.0 367.0] (70.0x82.0x180.0)",
+  "说明": "V2 L型结构：+Y侧背脊立柱避让大臂骨架，过渡区采用与顶板和立柱双相切的R=28mm平滑内凹大圆弧，彻底消除直斜线折角与悬空阶梯小块，顶板前后外缘2mm倒角改R3圆角，J4圆盘外沿与立柱外棱不倒圆保持原始尖角，下方M5电机半包散热，俯仰大范围自由运动零干涉"
  },
  {
   "件号": "P08_腕偏转座",