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/entity_renderer.gd

@@ -1,5 +1,5 @@
 class_name EntityRenderer
-extends Node2D
+extends GameplayRenderer
 
 # Entity renderer — manages entity sprites under the Entities node
 # Creates/updates/removes Sprite2D children based on entity data
@@ -35,11 +35,11 @@ var _entity_tweens: Dictionary = {}  # #521: entity_id -> {from: Color, target:
 var _entity_facing: Dictionary = {}  # #540: entity_id -> String ("north"/"east"/"south"/"west")
 
 
-func _ready() -> void:
+func _renderer_ready() -> void:
 	print("EntityRenderer: Initialized")
 
 
-func _process(delta: float) -> void:
+func _gameplay_process(delta: float) -> void:
 	# Lerp all entity visual positions toward their targets each frame.
 	# Uses framerate-independent exponential smoothing.
 	var weight := 1.0 - exp(-LERP_SPEED * delta)