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/actors/boss/boss_phase.gd

@@ -0,0 +1,18 @@
+class_name BossPhase
+extends Resource
+## One stage of a boss fight: a looping timeline of emitters, entered when the
+## boss drops below [member enter_at_hp_fraction].
+
+@export var name: String = "Phase"
+## The phase becomes active once hp/max_hp is at or below this. Phases are
+## evaluated in array order, so list them from 1.0 downwards.
+@export_range(0.0, 1.0, 0.01) var enter_at_hp_fraction: float = 1.0
+## The phase timeline wraps at this many ticks. Emitter [member start_tick] and
+## [member end_tick] are relative to the start of each loop.
+@export var loop_ticks: int = 600
+## Ticks of no fire after entering the phase, so the transition is readable.
+@export var telegraph_ticks: int = 45
+## Damage taken while in this phase is scaled by this. Use < 1.0 for armoured
+## phases rather than adding hit points, so the fight length stays predictable.
+@export var damage_taken_mult: float = 1.0
+@export var emitters: Array[BulletEmitter] = []