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/cursor_renderer.gd

@@ -1,5 +1,5 @@
 class_name CursorRenderer
-extends Node2D
+extends GameplayRenderer
 
 ## Cursor state machine — 4 geometric states, 150ms linear transitions (D-056).
 ## Insert-styled cursor on z-layer 7 (UILayer CanvasLayer).
@@ -54,7 +54,7 @@ var _bracket_a: float = 0.0
 var _alpha: float = 0.45
 
 
-func _ready() -> void:
+func _renderer_ready() -> void:
 	Input.set_mouse_mode(Input.MOUSE_MODE_HIDDEN)
 	z_index = 100  # D-170: cursor must always render above all HUD/implant layers
 	_from = _snapshot()
@@ -69,7 +69,7 @@ func _notification(what: int) -> void:
 		visible = true
 
 
-func _process(delta: float) -> void:
+func _gameplay_process(delta: float) -> void:
 	if not _mouse_inside:
 		return
 	_time += delta
@@ -243,8 +243,8 @@ func _interpolate() -> void:
 # --- Drawing ---
 
 
-func _draw() -> void:
-	# _hover_offset is computed in _detect_hover() during _process(), not recalculated
+func _gameplay_draw() -> void:
+	# _hover_offset is computed in _detect_hover() during _gameplay_process(), not recalculated
 	# here. This is safe because Camera2D (tree sibling, earlier in scene order) applies
 	# its smoothing transform before CursorRenderer._process() reads canvas_transform.
 	# Nothing modifies the canvas transform between _process() and _draw().