feat(ui): add relationship color accent to E-Talk overlay (#537)

Phase 1: interaction_list.gd shows a 3px left-edge accent bar in
D-033 relationship color (teal/green/amber/red) at 85% alpha.
Cross-references entity_id against visible_entities via
_cache_entity_relationship(). NPC name and tier hint deferred to
Phase 2 (requires server protocol extension).

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

client/ui/interaction_list.gd

@@ -29,6 +29,8 @@ var _verb_items: Array = []  # sorted [{kind, label, priority, available}]
 var _selected_index: int = 0
 var _active_tween: Tween = null
 var _verb_labels: Array[Label] = []
+# #537: D-033 relationship color — cached per target, drawn as left-edge accent bar
+var _relationship_color: Color = Constants.IMPLANT_TEXT_DIM
 
 @onready var _vbox: VBoxContainer = $VBox
 
@@ -52,6 +54,9 @@ func _draw() -> void:
 	var bg_rect := Rect2(-pad, -pad, size.x + pad * 2, size.y + pad * 2)
 	draw_rect(bg_rect, INSERT_BG)
 	draw_rect(bg_rect, Constants.IMPLANT_TEXT_DIM * Color(1, 1, 1, 0.3), false, 1.0)
+	# #537: D-033 relationship color accent — 3px left-edge bar signals NPC relationship
+	var bar_rect := Rect2(-pad, -pad, 3.0, bg_rect.size.y)
+	draw_rect(bar_rect, _relationship_color * Color(1, 1, 1, 0.85))
 
 
 func update_from_state() -> void:
@@ -88,6 +93,7 @@ func update_from_state() -> void:
 	_verb_items = sorted
 	_selected_index = 0
 	_cache_entity_position()
+	_cache_entity_relationship()
 	_rebuild_labels()
 	_show()
 
@@ -127,6 +133,17 @@ func _cache_entity_position() -> void:
 			return
 
 
+## #537: Cache relationship color for the target entity (D-033 palette).
+## Falls back to IMPLANT_TEXT_DIM for non-NPC or unknown entities.
+func _cache_entity_relationship() -> void:
+	for entity in GameState.visible_entities:
+		if entity.get("entity_id") == _current_target_id:
+			var rel: String = str(entity.get("relationship", "Unknown"))
+			_relationship_color = Constants.color_for_relationship(rel)
+			return
+	_relationship_color = Constants.IMPLANT_TEXT_DIM
+
+
 ## Convert entity world position to screen coords and reposition this Control.
 ## Runs every frame while showing so the list tracks the entity as the camera moves.
 func _update_screen_position() -> void: