fix(client): address PR #43 review — walk key mismatch + 5 suggestions

Fix SOUND_EVENT_ASSETS walk-speed keys to match actual filename
(sfx_footstep_metal_walk), add play_loop null guard, source indicator
colors from Constants, extract CAMERA_DEFAULT_ZOOM, document
consume-once semantics on close_sound_events.

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

client/scripts/rendering/sound_indicator_renderer.gd

@@ -26,10 +26,10 @@ const EDGE_INSET: float = 20.0          # Pixels inward from viewport edge
 const ARROW_HALF: float = 7.0           # Half-width of arrowhead base
 const ARROW_LEN: float = 12.0           # Length from tip to base
 
-# D-018/D-069 colors
-const COLOR_NEUTRAL: Color = Color("#c8d0e0")  # Generic / footstep
-const COLOR_VOICE: Color = Color("#e8c547")     # Speech / conversation
-const COLOR_DANGER: Color = Color("#d45d5d")    # Alert / threat / gunshot
+# D-018/D-069 colors — sourced from Constants to prevent palette drift
+const COLOR_NEUTRAL: Color = Constants.INSERT_COLOR_TEXT   # Generic / footstep
+const COLOR_VOICE: Color = Constants.ENTITY_COLOR_POI      # Speech / conversation
+const COLOR_DANGER: Color = Constants.ENTITY_COLOR_HOSTILE  # Alert / threat / gunshot
 
 # Indicators: [{x, y, event_type, elapsed}]
 var _indicators: Array = []
@@ -89,7 +89,7 @@ func _draw() -> void:
 	# the fog edge and don't clip to the physical screen border.
 	var vp_size := get_viewport().get_visible_rect().size
 	var cam := get_viewport().get_camera_2d()
-	var zoom := cam.zoom if cam else Vector2(2.0, 2.0)
+	var zoom := cam.zoom if cam else Constants.CAMERA_DEFAULT_ZOOM
 	var half_extents: Vector2 = vp_size / (2.0 * zoom)
 
 	for ind in _indicators: