feat(poc): implement Sprint 1 proof of concept

- project.godot with autoload configuration
- Reception room with placeholder visuals
- Draggable Character with DragDropComponent
- Interactive flower object with bounce animation
- GameState, SaveManager, AudioManager, InputManager autoloads
- HUD with back button and music toggle

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

scripts/systems/hud.gd

@@ -0,0 +1,21 @@
+## HUD — heads-up display with back button and music toggle.
+extends CanvasLayer
+
+var _music_enabled: bool = true
+
+
+func _ready() -> void:
+	pass
+
+
+func _on_back_button_pressed() -> void:
+	get_tree().quit()
+
+
+func _on_music_toggle_pressed() -> void:
+	_music_enabled = not _music_enabled
+	var volume: float = AudioManager.DEFAULT_MUSIC_VOLUME if _music_enabled else 0.0
+	AudioManager.set_music_volume(volume)
+	var btn: Button = get_node_or_null("MusicToggle") as Button
+	if btn != null:
+		btn.text = "♪" if _music_enabled else "✕"