feat(audio): Sprint 13 — AudioManager, zone crossfade, dip profiles, murmur wiring (#528, #529, #530, #533)

AudioManager: volume slider persistence (ConfigFile), settings UI with
5 teal-bordered sliders, default_bus_layout.tres for editor. Zone
crossfade: defensive zone_id read from snapshot tiles, 1.5-2s ambient
tween, auto-activates when server ships OQ-09. Dip profiles: dialogue
dip in show/hide_dialogue, ListeningFocus 30-tick gate via
stationary_ticks in game_state.gd. NPC murmur: client plumbing for
event-driven World SFX playback, no-ops until audio asset arrives.

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

client/scripts/autoloads/game_state.gd

@@ -62,6 +62,12 @@ var medium_sound_events: Array = []
 # Format: [{x, y, event_type, range_category}] — consumed once per tick in main.gd.
 var close_sound_events: Array = []
 
+# D-071 (#530): Consecutive ticks without player position change.
+# Incremented per snapshot in apply_snapshot(). Reset to 0 on movement.
+# ListeningFocus boost activates at 30+ ticks (main.gd manages the dip).
+var stationary_ticks: int = 0
+var _prev_player_position: Vector2 = Vector2(-1e9, -1e9)  # sentinel: no previous position
+
 func apply_snapshot(snapshot: Dictionary) -> void:
 	current_snapshot = snapshot
 
@@ -83,6 +89,14 @@ func apply_snapshot(snapshot: Dictionary) -> void:
 			push_warning("GameState: no Player entity found in %d entities" % [
 				visible_entities.size()])
 
+	# D-071 (#530): Track consecutive stationary ticks for ListeningFocus boost.
+	# Compares current player_position against previous snapshot's position.
+	if player_position == _prev_player_position:
+		stationary_ticks += 1
+	else:
+		stationary_ticks = 0
+	_prev_player_position = player_position
+
 	# Tiles for rendering: test mode sends "tiles", live server sends tile data in "visible_tiles"
 	if snapshot.has("tiles"):
 		visible_tiles = snapshot.tiles