fix(assets): address PR #96 review — all 8 items

- Fix stale 21→18 segment count in architecture doc, script docstrings,
  and disk budget table (critical — both reviewers)
- Add average_m/README.md noting role as clothing reference body
- Add __main__ guards to diagnostic scripts
- Preflight-check all source paths in blender_process_bodies.py
- Document solid-white hair masks as v0.2 placeholder for multi-region
- Add fallback size comment for head mask generation
- Add bald_mask.png (1×1 black) for sidecar convention consistency
- Document child non-uniform scale rationale (Y=0.72 vs XZ=0.75)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/architecture/character-asset-organization.md

@@ -116,7 +116,7 @@ client/assets/characters/
             seg_eyes.glb
             seg_eyebrows.glb
         thin_f/
-            ...                               # Same 21 segment files
+            ...                               # Same 18 segment files
         average_m/
             ...
         average_f/
@@ -134,7 +134,7 @@ client/assets/characters/
         heavy_f/
             ...
         child/                                # Gender-neutral, forked from Teen
-            ...                               # Same 21 segments but different proportions
+            ...                               # Same 18 segments but different proportions
     skin_tones/
         pale_cool.png                         # Skin tone texture variants
         pale_warm.png                         # Shared across all body types --
@@ -243,9 +243,9 @@ split from hair into their own directories because they are separate equip slots
 
 ### Why this structure
 
-**Bodies are directories, not flat files.** Each body type produces 21 segment GLBs (17 base
-+ 2 swappable torso variants + 2 face detail). Putting them in flat `bodies/` with prefixes
-(`thin_m_seg_head.glb`) would create 231 files in one directory. Directories per body type
+**Bodies are directories, not flat files.** Each body type produces 18 segment GLBs (14 limb/body
+segments + 2 torso variants + 2 face detail). Putting them in flat `bodies/` with prefixes
+(`thin_m_seg_head.glb`) would create 198 files in one directory. Directories per body type
 keep segment files scannable and let the compositor construct paths programmatically:
 `bodies/{body_type}/seg_{segment}.glb`.
 
@@ -292,7 +292,7 @@ underscore-separated, no abbreviations beyond `m`/`f`. The GDScript and Rust enu
 `ThinM`, `ThinF`, `AverageM`, `AverageF`, `MuscularM`, `MuscularF`, `TeenM`, `TeenF`,
 `HeavyM`, `HeavyF`, `Child`.
 
-### Body Segments (the 17 base + 2 swappable torso variants + 2 face detail)
+### Body Segments (14 limb/body segments + 2 torso variants + 2 face detail = 18 total)
 
 From the spike validation and D-160. Fine-grained segmentation is required for per-limb
 addressability: amputation (hide limb, show stump cap), prosthetics (replace limb with
@@ -342,7 +342,7 @@ boundary with the lower leg segment above ensures smooth deformation at the join
 The `seg_` prefix is load-bearing: it distinguishes segment GLBs from the `armature.glb` in
 the same directory and makes glob patterns simple (`seg_*.glb`).
 
-Total per body type: 17 base segments + 2 swappable torso variants + 2 face detail = **21 GLB files**.
+Total per body type: 14 limb/body segments + 2 torso variants (full and upper) + 2 face detail = **18 GLB files**.
 
 ### Clothing Items
 
@@ -472,7 +472,7 @@ no branching.
 | Animation libraries | **Shared** | 2+ GLBs | UAL1 (core) + UAL2 (extended + female mannequin); animations work on all body types via shared skeleton |
 | Shaders (toon, toon_masked, outline) | **Shared** | 3 files | One copy in `characters/shaders/` |
 | Skin tone textures | **Shared** | 9 PNGs | Toon shader tints these -- same textures for all body types |
-| Body segments | **Per body type** | 21 GLBs x 11 types = 231 | Each body type has its own segments (incl. swappable torso variants) |
+| Body segments | **Per body type** | 18 GLBs x 11 types = 198 | Each body type has its own segments (incl. swappable torso variants) |
 | Clothing items | **Per body type** | 11 GLBs + 1 reference + 1 mask + 1 coverage per item | Authored once on reference, batch-fitted to 11 |
 | Recolor masks (clothing) | **Shared per item** | 1 PNG per item | UV layout preserved through Surface Deform |
 | Coverage metadata | **Shared per item** | 1 JSON per item | Declares which segments to hide and torso variant selection |
@@ -509,7 +509,7 @@ Blender: fork/modify body shape (for thin, heavy, child -- 6 of 11 types)
        |-- OR: use as-is (average, muscular, teen -- 5 of 11 types)
        |
        v
-Blender: fine-grained segmentation (17 base + 2 swappable torso + 2 face detail = 21 GLBs)
+Blender: fine-grained segmentation (14 limb/body segments + 2 torso variants + 2 face detail = 18 GLBs)
        |
        v
 Export GLB (per segment / per clothing variant / per accessory)
@@ -666,7 +666,7 @@ and torso variant selection.
 |---|---|---|---|---|
 | Skeleton | 1 | 1 | 1 | ~10 KB |
 | Animations | 3 (UAL1 + UAL2 + future) | 1 | 3 | ~4 MB |
-| Body segments | 11 types | 21 segs | 231 | ~2.2 MB |
+| Body segments | 11 types | 18 segs | 198 | ~2.2 MB |
 | Skin tones | 1 set | 9 | 9 | ~500 KB |
 | Head templates | 50 (v0.2) | 2 (GLB+mask) | 100 | ~5 MB |
 | Hair styles | 18 (v0.2, Source tier) | 2 (GLB+mask) | 36 | ~1.8 MB |