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

src/sim/sim_boss.gd

@@ -0,0 +1,25 @@
+class_name SimBoss
+extends RefCounted
+## A boss instance. All fight-specific behaviour lives in its [BossDef]; this
+## class only advances the phase timeline.
+
+var id: int = 0
+var def: BossDef
+var pos := Vector2.ZERO
+var hp: int = 1
+var alive: bool = true
+var phase_index: int = 0
+## Ticks since entering the current phase.
+var phase_tick: int = 0
+
+
+func hp_fraction() -> float:
+	if def == null or def.max_hp <= 0:
+		return 0.0
+	return float(hp) / float(def.max_hp)
+
+
+func current_phase() -> BossPhase:
+	if def == null or def.phases.is_empty():
+		return null
+	return def.phases[clampi(phase_index, 0, def.phases.size() - 1)]