refactor(model): 重构P03为轻量化板式桁架并统一M4×16自攻螺钉连接方案

src/human_layout.py

@@ -48,8 +48,12 @@ SWEEP_R = 92.0             # farthest point of the humerus from the shoulder pit
 POD_R = 47.0               # saddle drum outer radius about the roll axis
 
 X_J1_HUB = 14.0            # J1 hub mating plane, forward of the humerus plate's ±44
-X_FORK_GAP = 0.0           # P04 前移量（用户裁定=0：前移会加大输出端悬伸弯矩，保持最短力臂）
-X_ARM = X_J1_HUB + PLATE_T / 2.0 + X_FORK_GAP   # 18.5 the limb's own plane in x
+X_BAY_EXT = 3.0            # M1 侧插槽加长量（2026-10-01 用户裁定：插槽开口 5.06+3=8.06，
+                           # 比电机前端面多 3mm 斜插余量；P03 托架前端 8.5+3=11.5）
+X_FORK_GAP = 1.0           # P04 肩叉前移量：叉板背面(10.5+1.0=11.5)与 P03 托架端面(11.5)
+                           # 0.0 硬贴平（2026-10-02 用户两次要求"搞成平的"，0.5mm 缝仍被判台阶）。
+                           # 注意：J1 相对转动时 M2 预紧会经此面产生摩擦阻力，若转动发涩可微松 M2。
+X_ARM = X_J1_HUB + PLATE_T / 2.0 + X_FORK_GAP   # 19.5 the limb's own plane in x
 Z_R1 = X_J1_HUB - HUB      # -51  J1 rear datum, measured in x: M1 lies behind the shoulder
 Z_CHEST1 = Z_RL - 140.0    # 470 torso mast top
 Z_CHEST0 = FOOT_H