bootstrap: finish project bootstrap — scale test, MPFB character, build docs

- Static-mesh scale test passes: 1 m = 100.00 cm, origin preserved, axis
  mapping east→+X / north→−Y / up→+Z (named presets ue_metric_v1 both sides).
- MPFB 2.0.18 acceptance passes: generated human + standard 137-bone rig
  with weights + v2 skin baked to 1024² diffuse; imports as SkeletalMesh
  with Skeleton, Material, and Texture2D in /Game/Test/Character.
- MPFB headless requires XDG_CONFIG_HOME at the Flatpak config tree;
  documented in Art/blender/README.md, probe in Tools/addon_compat_probe.py.
- Docs/build.md completed: fresh-checkout build, packaging, headless checks.
- Docs/setup.md reconciled with reality; ROADMAP/bootstrap closed out.

Tools/addon_compat_probe.py

@@ -0,0 +1,64 @@
+# Headless compatibility probe for Blosm and MPFB on the pinned Blender 5.2.
+#
+#   blender -b --factory-startup --python Tools/addon_compat_probe.py
+#
+# Checks: Blender version, Blosm add-on loads + version, MPFB extension
+# enables + version, MPFB can create a default human headless, resulting
+# object inventory (mesh/armature/materials/uvs).
+
+import bpy
+import sys
+
+REPORT = "/tmp/addon-compat-report.txt"
+lines = []
+
+
+def log(msg):
+    lines.append(str(msg))
+
+
+bl = bpy.app.version_string
+log(f"Blender: {bl}")
+
+# --- Blosm (legacy add-on, scripts/addons) ---
+try:
+    import blosm  # noqa
+    info = getattr(blosm, "bl_info", {})
+    log(f"blosm: import OK, version {info.get('version', '?')}, blender {info.get('blender', '?')}")
+except Exception as exc:  # noqa
+    log(f"blosm: IMPORT FAILED: {exc!r}")
+
+# --- MPFB (extension, extensions/blender_org/mpfb) ---
+try:
+    import addon_utils
+    bpy.ops.preferences.addon_enable(module="bl_ext.blender_org.mpfb")
+    enabled = "bl_ext.blender_org.mpfb" in bpy.context.preferences.addons
+    version = "?"
+    try:
+        import bl_ext.blender_org.mpfb as mpfb_mod
+        version = getattr(mpfb_mod, "MPFB_VERSION", "?")
+    except Exception:
+        pass
+    log(f"mpfb: enable OK (registered={enabled}), version {version}")
+except Exception as exc:  # noqa
+    log(f"mpfb: ENABLE FAILED: {exc!r}")
+
+# --- MPFB create-human smoke test ---
+try:
+    bpy.ops.mpfb.create_human("EXEC_DEFAULT")
+    meshes = [o for o in bpy.data.objects if o.type == "MESH"]
+    armatures = [o for o in bpy.data.objects if o.type == "ARMATURE"]
+    log(f"mpfb.create_human: OK — {len(bpy.data.objects)} objects, "
+        f"{len(meshes)} meshes, {len(armatures)} armatures")
+    for o in meshes:
+        uv = bool(o.data.uv_layers)
+        mats = [m.name for m in o.data.materials]
+        log(f"  mesh {o.name}: {len(o.data.vertices)} verts, uv={uv}, materials={mats}")
+    for o in armatures:
+        log(f"  armature {o.name}: {len(o.data.bones)} bones")
+except Exception as exc:  # noqa
+    log(f"mpfb.create_human: FAILED: {exc!r}")
+
+with open(REPORT, "w") as f:
+    f.write("\n".join(lines) + "\n")
+print("\n".join(lines))