fix(pipeline): stand the character up before scaling; reach bones by role

Fixes the two root causes behind four of the seven reported breakages, and
rejects the source that cannot be fixed.

STAND UP FIRST. flatten_and_scale() now derives the up axis from the
skeleton and rotates the model upright before measuring anything. Aria and
Momo are correct: 1.75 m tall, 1.43 x 0.41 and 1.52 x 0.39 across, verified
by render.

The up vector is measured from the FEET to the HIPS, not from the hips to
the head. The head is not a reliable landmark — the spine walk ends on the
last non-cosmetic bone in the chain, which on a rig with a facial skeleton
can sit BELOW the hips. Momo's did, so the first cut of this fix stood her
neatly on her head: right size, right proportions, upside down. Feet cannot
be mistaken.

REACH BONES BY ROLE. SkinnedPlayerModel gained _role_bone(), and set_weapon
uses it. Four characters could not hold a gun because one hardcoded lookup
knew three spellings and their hands are called "Right wrist" and
"J_Bip_R_Hand" — both resolved perfectly in the sidecar the whole time.

HIKARI IS REJECTED. She now fails the gate: her feet and spine disagree
about which way is up, so the stand-up correction cannot resolve her
either, on top of zero-length cosmetic bones and a second armature that was
smuggling its own clips into the export. That is not a tuning problem, it
is a file that has been through two toolchains. De-registered and removed
rather than shipped broken — which is what the gate is for.

Six GLB skins remain, all passing. Smoke 0 failures, 11/11 movement tests.

Still open, recorded in the skill: kiyoko faces backwards, miku's grown
hair stretches under animation, the mannequin's rifle hold does not
convince, and taila's front skirt clipping.

Co-Authored-By: Claude Opus 5 <[email protected]>

assets/characters/skins/skins.json

@@ -41,13 +41,6 @@
       "description": "Momo Ayase, DANDADAN (CC-BY, HiGuys920)",
       "model": "res://assets/characters/skins/momo.glb",
       "unlocked": true
-    },
-    {
-      "id": "hikari",
-      "name": "Hikari",
-      "description": "School anime girl \u2014 VRoid (CC-BY, hikari)",
-      "model": "res://assets/characters/skins/hikari.glb",
-      "unlocked": true
     }
   ]
 }