feat(ui): implement dialogue pipeline — selection, walk-away, confrontation

Protocol: decode current_dialogue with structured options {text,
response_id, priority, confrontation} and npc_entity_id (#435).
Dialogue box: priority sort, max 3 visible, RichTextLabel for BBCode
italic confrontation options (D-063), 1.5s monologue beat with audio
dip before confrontation send. Walk-away: WASD triggers WalkAway
input, 300ms fade, dialogue_active flag gates movement (D-064).
Implements #435, #437, #436.

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

client/scripts/autoloads/game_state.gd

@@ -29,8 +29,12 @@ var current_monologue: Variant = null  # {id, text, duration_seconds} or null
 var player_stance: String = "Walk"  # Sprint/Walk/Careful/Crouch
 var player_inventory: Array = []  # [{item_id, name, slot}]
 
-# v7 fields (#434, D-061)
-var current_dialogue: Variant = null  # {npc_name, speech, options: [String]} or null
+# v7 fields (#435, D-061/D-062)
+var current_dialogue: Variant = null  # {npc_name, npc_entity_id, speech, options: [{text, response_id, priority}]} or null
+
+# D-064: true while dialogue box is visible or fading out (300ms).
+# InputMapper suppresses movement when this is true.
+var dialogue_active: bool = false
 
 # v7 fields (#431, D-059/D-060)
 var pending_recognitions: Array = []  # [{entity_id, x, y, z, remaining_ticks, total_delay_ticks}]