refactor: organise assets, tidy player.gd, unbreak fresh import

Assets grouped by role, within the constraint that FBX materials resolve
their textures by path relative to the FBX itself (verified by forcing a
reimport and reading back the albedo paths):

  assets/level/   scene.fbx + Level1_v1.fbx + the platform maps they look
                  up as siblings
  assets/logos/   the three attribution logos
  assets/         chara_red.fbx, background.fbx — these reach up into
                  ../sourceimages and so cannot move
  sourcefiles/    scene.blend, behind a .gdignore

The .blend move is a bug fix, not tidying. Godot hands every importable
.blend to a headless Blender, and that call never returns on this project
— a fresh clone stalls on first import, and the machine still had orphaned
Blender processes from an earlier attempt. Nothing loads the .blend: the
level geometry is baked into level_1.tscn.

player.gd: spell out ct/bt/d/ix/a, type the physics step, group the
members, and point the blue skin at sourceimages/low_blue_mat_* — the same
files assets/Chara_blue/ was a byte-identical copy of.

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

assets/level/Level1_v1.fbx.import

@@ -0,0 +1,46 @@
+[remap]
+
+importer="scene"
+importer_version=1
+type="PackedScene"
+uid="uid://cvu5f82j7vxdl"
+path="res://.godot/imported/Level1_v1.fbx-057b7bbcfd96046aa01265df55d6c0f0.scn"
+
+[deps]
+
+source_file="res://assets/level/Level1_v1.fbx"
+dest_files=["res://.godot/imported/Level1_v1.fbx-057b7bbcfd96046aa01265df55d6c0f0.scn"]
+
+[params]
+
+nodes/root_type=""
+nodes/root_name=""
+nodes/root_script=null
+mesh_library/use_node_names_as_mesh_names=false
+array_mesh/deduplicate_surfaces=true
+nodes/apply_root_scale=true
+nodes/root_scale=1.0
+nodes/import_as_skeleton_bones=false
+nodes/use_name_suffixes=true
+nodes/use_node_type_suffixes=true
+meshes/ensure_tangents=true
+meshes/generate_lods=true
+meshes/create_shadow_meshes=true
+meshes/light_baking=1
+meshes/lightmap_texel_size=0.2
+meshes/force_disable_compression=false
+skins/use_named_skins=true
+animation/import=true
+animation/fps=30
+animation/trimming=true
+animation/remove_immutable_tracks=true
+animation/import_rest_as_RESET=false
+import_script/path=""
+materials/extract=0
+materials/extract_format=0
+materials/extract_path=""
+_subresources={}
+fbx/importer=0
+fbx/allow_geometry_helper_nodes=false
+fbx/embedded_image_handling=1
+fbx/naming_version=2