fix: connect vertex-weight-limit's arm parts and straighten the reach

[TMHSDigital]

Summary

Round two on the vertex-weight-limit hero, addressing the maintainer's read: overflow, overlap, spaces that shouldn't be there.

Defects and fixes (each structural, verified in pixels):

• Overlap — floating discs. The shoulder hub's caps read as wheels stuck on the shell; the hinge caps floated off the joint with a visible gap. The hub is removed and the upper arm is now rooted deep inside the shoulder fairing (the -8° shoulder articulation cannot open a gap — the root ring stays interpenetrated). Hinge caps now sit flush on the clevis cheeks as bolt heads.
• Spaces — detached parts. Fingers hung 0.05 above a hidden palm: the palm now grows into the finger roots (roots inside the palm span). The bellows recessed at both ends leaving dark grooves: end radii now match the shells they join (0.21 upper arm, 0.19 forearm; 0.18/0.17 at the wrist), reading as continuous ribbed sleeves over the joints.
• Overflow — claw jammed at the top. Wrist -18°→-14°, Claw +12°→+6° straightens the reach. Verified numerically, not by eyeballing a downsample: posed-vertex NDC projection puts the claw 103 px inside the top edge; the subject mask bbox confirms margins on all sides (the only negative-NDC geometry is the fairing's below-floor sink, occluded by the floor — planted, not clipped).

Check contracts unchanged: pre_max=5 holds; measured values identical on .scratch/blender-5.1.2-windows-x64/blender.exe (Blender 5.1.2) and .scratch/blender-4.5.11-windows-x64/blender.exe (Blender 4.5.11 LTS): verts=1856 pre=5 post=4 limited=128 sum_err=2.98e-08 pose_dev=2.80e-03 lbs_err=2.98e-07 root_move=0. Re-falsified: probe A exit 4, probe B exit 6 (sums 1.269e-02), probe C exit 8 (LBS dev 1.777). No tolerance loosened. 4.5 render path green.

Refreshed group contact sheet (luminance 111.9, in set range). README intro updated (no more "shoulder hub"); gallery rebuilt and detail HTML re-read.

Test plan

• Validate, manifest, counts
• Blender 5.1 + 4.5 smoke (vertex-weight-limit step)

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