feat(clothing): tee, jeans and shoes as separate skinned meshes

Follows the character-artist clothing workflow literally: duplicate the body's own
faces for the garment base, solidify for cloth thickness, and keep each piece a
separate mesh. Attached as leader-pose components beside the hair, so no second rig.

- Tools/character_clothing_build.py builds three garments from the body mesh, trimmed
  geometrically (height band plus a width limit) instead of by dominant bone: the bone
  filter left holes wherever a face's strongest bone was outside the allowed list.
- Tools/ue_character_clothing_import.py imports them as CharacterTee / CharacterJeans /
  CharacterShoes, each arriving with its own single material slot.
- The pawn attaches all three, hidden with the body in first person.

Three traps recorded in MEMORY.md, each of which cost a build: MPFB weights its helper
geometry to groups that dominate every vertex, Blender refuses to apply a modifier to a
mesh with shape keys, and object-mode polygon selection is discarded on entering edit
mode - the delete wiped the whole garment.

Known defects, in TODO.md: the garments have coverage holes at shoulders, hips and
knees, and the hair reads light and wispy since its material was repointed to the
masked strand sheet.

MEMORY.md

@@ -505,3 +505,6 @@ Scope: facts and traps that cost time to establish. Planned work lives in [TODO.
 - **Segmenting the character out of a review shot does not work by colour.** The sky band, the pale wall and the dark pavement are each larger and more saturated than the body, so every size-based rule picked a backdrop blob and the first report measured the whole frame. `Tools/character_match.py` now takes an explicit `--render-box`; the proper fix is a background plate rendered without the character.
 - **The report has to separate the failures it measures.** Aspect, fill, coverage and two colour distances are reported apart on purpose: an absolute similarity number between a photoreal sheet and a low-detail body would mean nothing. The first real comparison (aspect Δ1.24, mean ΔE 31.9) was dominated by the model being **unclothed** while the blueprint wears a tee and jeans.
 - **`SetMaterial(0, ...)` in the pawn constructor does not visibly land** on the body mesh: `M_Character_Skin` is built and assigned, yet the render stays neutral grey. Either the slot does not exist yet at that point or the assignment is dropped; `BeginPlay` is the next thing to try.
+- **MPFB vertex groups are polluted by helper geometry.** The body mesh weights its helper cubes to groups named `Left`, `Right`, `HelperGeometry` and `JointCubes` at 1.0, so a "strongest group" lookup returns a helper for most vertices - the first clothing build selected **zero** faces. Filter helper names out before asking which bone a vertex belongs to.
+- **Blender refuses to apply a modifier to a mesh with shape keys.** The body carries ten; a garment copy must clear them (`shape_key_remove(all=True)`) before solidify can be applied.
+- **Edit-mode selection reverts to vertex selection.** Setting `polygon.select` in object mode and then entering edit mode re-derives selection from the vertices, which were all still selected - deleting "the unselected faces" wiped the entire garment. Filter with `bmesh.ops.delete(context="FACES")` instead.