feat: Implement nausea symptom system and related features

- Added SymptomManager autoload for managing symptom intensities.
- Introduced nausea tilt effect for camera roll based on nausea intensity.
- Created color desaturation shader and overlay for visual feedback.
- Developed TreatmentManager to handle nausea ramping during IV treatment.
- Added hospital room scene with first-person controller and interactions.
- Implemented sit-down interaction for the treatment chair.
- Created IV insertion sequence with animations and completion signal.
- Added player controller with movement and interaction capabilities.
- Integrated nausea effects into the player experience with smooth transitions.

scripts/symptoms/nausea_tilt.gd

@@ -0,0 +1,48 @@
+extends Camera3D
+## Nausea screen-tilt effect.
+##
+## Rolls the camera slightly on its local Z axis, oscillating over time, with
+## amplitude proportional to nausea intensity. Attach to the player `Camera3D`.
+## The first-person controller only writes camera rotation.x (pitch), so writing
+## rotation.z here does not conflict.
+
+## Maximum tilt in degrees at full nausea (100).
+@export var max_tilt_deg: float = 5.0
+## Oscillation frequency in Hz.
+@export var frequency_hz: float = 0.3
+## How fast the effective intensity follows the target, in intensity units/sec.
+## At 200, a full 0->100 change resolves in ~0.5s.
+@export var intensity_follow_speed: float = 200.0
+
+var _target_intensity: float = 0.0
+var _current_intensity: float = 0.0
+var _time: float = 0.0
+
+
+func _ready() -> void:
+	# Resolve the SymptomManager autoload via the scene tree root when possible,
+	# falling back to the global autoload identifier.
+	var sm: Node = null
+	if is_inside_tree():
+		sm = get_tree().root.get_node_or_null("SymptomManager")
+	if sm == null:
+		sm = SymptomManager
+	if sm:
+		sm.nausea_intensity_changed.connect(_on_nausea_changed)
+		_target_intensity = sm.get_intensity(sm.NAUSEA)
+		_current_intensity = _target_intensity
+
+
+func _on_nausea_changed(value: float) -> void:
+	_target_intensity = value
+
+
+func _process(delta: float) -> void:
+	_time += delta
+	_current_intensity = move_toward(
+		_current_intensity, _target_intensity, intensity_follow_speed * delta
+	)
+
+	var amplitude := deg_to_rad(max_tilt_deg) * (_current_intensity / 100.0)
+	var roll := sin(_time * TAU * frequency_hz) * amplitude
+	rotation.z = roll