Initial commit: Transcience MVP

Top-down twin-stick bullet-hell, Godot 4.7, server-authoritative dedicated
server with client-side prediction. Clients send input only; the server
resolves every hit for both players and enemies (no PvP).

- SimWorld: whole simulation as plain RefCounted objects (no nodes, no
  physics server), ~0.24ms/tick at peak load -- runs headless for free and
  drives 78 tests in under a second
- BulletPool: struct-of-arrays bullet storage, replicated as spawn/despawn
  events rather than per-tick state
- Emitter framework (Ring/AimedSpread/WallGap/ArcSweep) shared by trash
  enemies and bosses -- a new boss is data in src/content/content.gd, no
  simulation changes
- The Warden of the Fold: stationary 4-phase boss built entirely on that
  format
- Lobby hub with a portal into on-demand dungeon instances; one process
  hosts the hub plus every concurrent dungeon
- Emergency escape: 3s server-owned channel, cancelled by damage
- tools/check.sh, test.sh (GUT), smoke.sh (real server + bot clients over
  ENet), bench.gd; git hooks wired to the same scripts
- docs/ARCHITECTURE.md, NETCODE.md, WORKFLOW.md, ROADMAP.md

tools/export_content.gd

@@ -0,0 +1,36 @@
+extends SceneTree
+## Writes .tres copies of everything in [Content] into res://resources/, so the
+## numbers can be tuned in the editor inspector.
+##
+##   godot --headless --path . --script tools/export_content.gd
+##
+## These files are an export, not the source of truth: [Content] is. Re-running
+## this overwrites them. If you tune a value in the inspector and want to keep
+## it, port it back into src/content/content.gd -- otherwise the next export
+## silently reverts your change.
+
+const OUT_ENEMIES := "res://resources/enemies"
+const OUT_BOSSES := "res://resources/bosses"
+
+
+func _init() -> void:
+	DirAccess.make_dir_recursive_absolute(OUT_ENEMIES)
+	DirAccess.make_dir_recursive_absolute(OUT_BOSSES)
+	var written := 0
+	for id in [Content.ENEMY_DRIFTER, Content.ENEMY_TURRET, Content.ENEMY_STALKER,
+			Content.ENEMY_DUMMY]:
+		written += _save(Content.enemy(id), "%s/%s.tres" % [OUT_ENEMIES, id])
+	for id in [Content.BOSS_WARDEN]:
+		written += _save(Content.boss(id), "%s/%s.tres" % [OUT_BOSSES, id])
+	print("exported %d resources" % written)
+	quit(0)
+
+
+func _save(res: Resource, path: String) -> int:
+	# Sub-resources (the emitters) are inlined so one file is one whole enemy.
+	var err := ResourceSaver.save(res, path)
+	if err != OK:
+		printerr("failed to write %s (error %d)" % [path, err])
+		return 0
+	print("  ", path)
+	return 1