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/scripts/export_tb_config.gd

@@ -0,0 +1,97 @@
+extends SceneTree
+
+# Usage:
+#   godot --headless --path demo --script scripts/export_tb_config.gd -- OUT_DIR
+#
+# Writes a complete TrenchBroom game config to OUT_DIR:
+#   OUT_DIR/GameConfig.cfg   — game definition (name, formats, texture dirs)
+#   OUT_DIR/FuncGodot.fgd    — entity definitions, generated from
+#                              res://data/fgd/brogue_fgd.tres via
+#                              FuncGodotFGDFile.build_class_text().
+#
+# Skips the Inspector's "Export FGD" button entirely. Safe to re-run after
+# any change to brogue_fgd.tres or entity resources under data/entities/.
+
+const GAME_CONFIG := """{
+\t\"version\": 9,
+\t\"name\": \"brogue-genesis\",
+\t\"icon\": \"icon.png\",
+\t\"fileformats\": [
+\t\t{ \"format\": \"Valve\", \"initialmap\": \"initial_valve.map\" },
+\t\t{ \"format\": \"Standard\", \"initialmap\": \"initial_standard.map\" }
+\t],
+\t\"filesystem\": {
+\t\t\"searchpath\": \".\",
+\t\t\"packageformat\": { \"extension\": \".zip\", \"format\": \"zip\" }
+\t},
+\t\"materials\": {
+\t\t\"root\": \"textures\",
+\t\t\"extensions\": [\".bmp\", \".jpeg\", \".jpg\", \".png\", \".tga\", \".webp\"],
+\t\t\"excludes\": [ \"*_albedo\", \"*_ao\", \"*_emission\", \"*_height\", \"*_metallic\", \"*_normal\", \"*_orm\", \"*_roughness\", \"*_sss\" ],
+\t\t\"palette\": \"textures/palette.lmp\",
+\t\t\"attribute\": \"wad\"
+\t},
+\t\"entities\": {
+\t\t\"definitions\": [ \"FuncGodot.fgd\" ],
+\t\t\"defaultcolor\": \"0.6 0.6 0.6 1.0\",
+\t\t\"scale\": 32
+\t},
+\t\"tags\": {
+\t\t\"brush\": [],
+\t\t\"brushface\": [
+\t\t\t{ \"name\": \"Clip\", \"attribs\": [ \"transparent\" ], \"match\": \"material\", \"pattern\": \"clip\" },
+\t\t\t{ \"name\": \"Skip\", \"attribs\": [ \"transparent\" ], \"match\": \"material\", \"pattern\": \"skip\" },
+\t\t\t{ \"name\": \"Origin\", \"attribs\": [ \"transparent\" ], \"match\": \"material\", \"pattern\": \"origin\" }
+\t\t]
+\t},
+\t\"faceattribs\": {
+\t\t\"defaults\": { \"scale\": [1.0, 1.0] },
+\t\t\"contentflags\": [],
+\t\t\"surfaceflags\": []
+\t}
+}
+"""
+
+func _init() -> void:
+	var args := OS.get_cmdline_user_args()
+	if args.size() != 1:
+		push_error("usage: -- OUT_DIR")
+		quit(1)
+		return
+	var out_dir: String = args[0]
+
+	if not DirAccess.dir_exists_absolute(out_dir):
+		if DirAccess.make_dir_recursive_absolute(out_dir) != OK:
+			push_error("failed to create %s" % out_dir)
+			quit(1)
+			return
+
+	var cfg_path := out_dir.path_join("GameConfig.cfg")
+	var cfg_file := FileAccess.open(cfg_path, FileAccess.WRITE)
+	if cfg_file == null:
+		push_error("cannot open %s for write" % cfg_path)
+		quit(1)
+		return
+	cfg_file.store_string(GAME_CONFIG)
+	cfg_file.close()
+
+	var fgd: Resource = load("res://data/fgd/brogue_fgd.tres")
+	if fgd == null:
+		push_error("failed to load res://data/fgd/brogue_fgd.tres")
+		quit(1)
+		return
+
+	var fgd_text: String = fgd.build_class_text(1)  # 1 == TRENCHBROOM
+	var fgd_path := out_dir.path_join("FuncGodot.fgd")
+	var fgd_file := FileAccess.open(fgd_path, FileAccess.WRITE)
+	if fgd_file == null:
+		push_error("cannot open %s for write" % fgd_path)
+		quit(1)
+		return
+	fgd_file.store_string(fgd_text)
+	fgd_file.close()
+
+	print("synced TrenchBroom config to %s" % out_dir)
+	print("  GameConfig.cfg  %d bytes" % GAME_CONFIG.length())
+	print("  FuncGodot.fgd   %d bytes" % fgd_text.length())
+	quit(0)