feat(rendering): GameplayRenderer base class — occlusion for all renderers (D-170)

New GameplayRenderer extends Node2D with built-in occlusion support.
Subclasses override _gameplay_process() and _gameplay_draw() instead
of _process() and _draw() — these are skipped when a fullscreen
implant app covers gameplay.

Migrated all 5 gameplay renderers:
- CursorRenderer: hover detection + bracket drawing paused
- EntityRenderer: position lerping paused
- FogEntities: fog dot rendering paused
- SoundIndicatorRenderer: directional arrows paused
- WorldRenderer: tile/fog/entity updates paused

No more manual occlusion wiring — the base class handles everything.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client/scripts/rendering/sound_indicator_renderer.gd

@@ -1,5 +1,5 @@
 class_name SoundIndicatorRenderer
-extends Node2D
+extends GameplayRenderer
 
 ## Medium-range sound indicators (#126, D-018).
 ## Renders directional arrows at the fog boundary for sounds outside LOS.
@@ -35,7 +35,7 @@ const COLOR_DANGER: Color = Constants.ENTITY_COLOR_HOSTILE  # Alert / threat / g
 var _indicators: Array = []
 
 
-func _process(delta: float) -> void:
+func _gameplay_process(delta: float) -> void:
 	if _indicators.is_empty():
 		return
 
@@ -84,7 +84,7 @@ func update_sound_events(events: Array) -> void:
 		queue_redraw()
 
 
-func _draw() -> void:
+func _gameplay_draw() -> void:
 	if _indicators.is_empty():
 		return