Tattoo test bed: Quaternius v3-v6 bakes + Lena pipeline (bake, de-mirror, re-UV, viewers)

Session 2026-07-23/24 additions on top of the existing Quaternius bed:
- bake_lena.gd: 6-piece bake on QuatSkin Lena (chiefs-mark/iron-spine arms,
  voyagers/storm-bearer legs, star-eye chest, hearth-warmth back); global-axis
  wrap frame + 3cm junction blend kill the elbow split line
- demirror_lena.gd: tri-level split of mirror-shared limb UVs (arms 100%->0%,
  legs 99%->5% crotch-only residual)
- reuv_lena.gd: Quaternius-style semantic re-UV (16 islands, cylinder limbs +
  cylinder head/torso with planar caps) + texture transfer; fixes armpit/chin/
  cheek planar smears; single 4096 atlas, per-side tattoos native
- main_lena / anim_lena viewers (18 UAL clips, U light toggle) + probes + shots

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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