feat(particles): bubble trail behind dolphin + block break burst

- BubbleTrail.gd: GPUParticles3D, auto-configured in _ready, set_intensity() API
- BlockBreakParticles.gd: one_shot burst, emit_burst(pos, color) API
- DolphinController.gd: bubble_trail onready + speed_factor hook in _update_movement
- Dolphin.tscn: BubbleEmitterPoint (0,0,1.2) > BubbleTrail child added

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/dolphin/BubbleTrail.gd

@@ -0,0 +1,52 @@
+extends GPUParticles3D
+
+func _ready() -> void:
+	amount = 80
+	lifetime = 1.5
+	emitting = false
+	local_coords = false
+
+	var mat := ParticleProcessMaterial.new()
+	mat.direction = Vector3(0.0, 0.3, 0.0)
+	mat.initial_velocity_min = 0.5
+	mat.initial_velocity_max = 1.5
+	mat.spread = 15.0
+	mat.gravity = Vector3(0.0, 0.5, 0.0)
+	mat.scale_min = 0.03
+	mat.scale_max = 0.12
+
+	var scale_curve := Curve.new()
+	scale_curve.add_point(Vector2(0.0, 0.2))
+	scale_curve.add_point(Vector2(0.5, 1.0))
+	scale_curve.add_point(Vector2(1.0, 0.0))
+	var scale_curve_tex := CurveTexture.new()
+	scale_curve_tex.curve = scale_curve
+	mat.scale_curve = scale_curve_tex
+
+	mat.color = Color(1.0, 1.0, 1.0, 0.6)
+	process_material = mat
+
+	var sphere := SphereMesh.new()
+	sphere.radius = 0.05
+	sphere.height = 0.1
+	sphere.rings = 4
+	sphere.radial_segments = 6
+
+	var bubble_mat := StandardMaterial3D.new()
+	bubble_mat.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
+	bubble_mat.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA
+	bubble_mat.albedo_color = Color(1.0, 1.0, 1.0, 0.55)
+	bubble_mat.emission_enabled = true
+	bubble_mat.emission = Color(0.8, 0.9, 1.0, 1.0)
+	bubble_mat.emission_energy_multiplier = 0.3
+	sphere.surface_set_material(0, bubble_mat)
+
+	draw_pass_1 = sphere
+
+
+func set_intensity(speed_factor: float) -> void:
+	if speed_factor > 0.5:
+		emitting = true
+		amount_ratio = clamp(speed_factor / 1.5, 0.3, 1.0)
+	else:
+		emitting = false