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/core/movement.gd

@@ -0,0 +1,31 @@
+class_name Movement
+extends RefCounted
+## Pure movement helpers. These run on the server (authoritative) and on the
+## client (prediction). They must stay side-effect free so a client can replay
+## them over a history of inputs and land on the same result as the server.
+
+## Clamp a raw analogue/keyboard vector to a unit disc.
+static func sanitize_move(raw: Vector2) -> Vector2:
+	if raw.length_squared() > 1.0:
+		return raw.normalized()
+	return raw
+
+
+## One tick of player locomotion. Returns the new position.
+static func step_player(pos: Vector2, move: Vector2, speed: float, bounds: Vector2) -> Vector2:
+	var next := pos + sanitize_move(move) * speed * SimConfig.TICK_DELTA
+	next.x = clampf(next.x, -bounds.x, bounds.x)
+	next.y = clampf(next.y, -bounds.y, bounds.y)
+	return next
+
+
+## Circle-vs-circle overlap test used for every hit in the game.
+static func circles_overlap(a: Vector2, ar: float, b: Vector2, br: float) -> bool:
+	var r := ar + br
+	return a.distance_squared_to(b) <= r * r
+
+
+## True when a point has drifted outside the arena plus the cull margin.
+static func outside_arena(p: Vector2, margin: float = SimConfig.BULLET_CULL_MARGIN) -> bool:
+	return absf(p.x) > SimConfig.ARENA_HALF.x + margin \
+		or absf(p.y) > SimConfig.ARENA_HALF.y + margin