feat: 3D blobber dungeon generator (PR 1)

Replaces the 2D-only demo pipeline with a 3D cell-based blobber
generator. Per-cell face walls, per-material mesh emission, and a
GDExtension binding that returns a Dictionary with ArrayMesh surfaces
the demo consumes directly.

- src/blobber/: cell3d_t data model, dungeon container, pipeline that
  wraps the 2D generator per level and materializes into cell3d
- src/mesh/: face-quad emitter with per-material groups + .obj dump
- src/genesis3d_main.c: new CLI driving the blobber + mesh
- godot/: BrogueGen.generate_dungeon(seed, num_levels, depth) binding
  with dungeon_to_dict packing cells + mesh surfaces
- demo/: demo_blobber.tscn + dungeon_builder.gd, func_godot addon for
  the .map export path, point/entity templates, TrenchBroom docs
- Retired: old arcade/FPS demo scenes and their scripts, unused meshlib

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

demo/scenes/dungeon_from_map.tscn

@@ -0,0 +1,17 @@
+[gd_scene format=3 uid="uid://bq41mttbygl2a"]
+
+[ext_resource type="Script" uid="uid://cwu5cf7a0awcd" path="res://addons/func_godot/src/map/func_godot_map.gd" id="1_map_script"]
+[ext_resource type="Resource" path="res://data/config/brogue_map_settings.tres" id="2_map_settings"]
+
+[node name="DungeonFromMap" type="Node3D" unique_id=693515113]
+
+[node name="FuncGodotMap" type="Node3D" parent="." unique_id=858233376]
+script = ExtResource("1_map_script")
+local_map_file = "res://maps/generated.map"
+map_settings = ExtResource("2_map_settings")
+
+[node name="Camera3D" type="Camera3D" parent="." unique_id=125559999]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 50, 100)
+
+[node name="DirectionalLight3D" type="DirectionalLight3D" parent="." unique_id=391021715]
+transform = Transform3D(1, 0, 0, 0, 0.707, 0.707, 0, -0.707, 0.707, 0, 10, 0)