feat(ui): add in-game debug console with tilde toggle and command dispatch (#581)

- debug_console.gd: new ModalLayer Control — tilde key toggles bottom-40% panel,
  command history (up/down), SimBridge dispatch for all DebugCommandKind variants:
  ticks, contaminate, tp, activate, triangle, npc, triangles, pop, status, help
- debug_console.tscn: minimal scene node; UI built programmatically in _ready()
- input_mapper.gd: DEBUG_COMMAND action added to Action enum
- sim_bridge.gd: DEBUG_COMMAND → "DebugCommand" wire mapping
- protocol.gd: v18 debug_response decode (command, text, success fields)
- game_state.gd: debug_response field + apply_snapshot one-shot handling
- main.gd: @onready ref, router registration, _consume_debug_response(), settings signal
- settings_dialog.gd: debug_console_toggled signal + CheckButton toggle row (+36px height),
  reads initial state from user://settings.cfg; CheckButton state loaded from PREFS_PATH
- main.tscn: DebugConsole node on ModalLayer, load_steps 27→28

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

client/scripts/main.gd

@@ -22,6 +22,7 @@ extends Node2D
 @onready var bug_report_dialog = $ModalLayer/BugReportDialog  # #495: F12 WRONG button
 @onready var settings_dialog = $ModalLayer/SettingsDialog     # #528: audio settings (ESC/OPEN_MENU)
 @onready var loading_screen = $ModalLayer/LoadingScreen       # #257: blocking overlay during load
+@onready var debug_console = $ModalLayer/DebugConsole         # #581: tilde debug console
 
 var _last_dialogue_npc_id: int = -1  # D-064: NPC entity_id for WalkAway input
 var _last_dialogue_npc_name: String = ""  # #535: NPC name for dialogue_response attribution
@@ -122,6 +123,11 @@ func _ready() -> void:
 	_router.register("conversation_ended", _consume_conversation_ended)
 	_router.register("dialogue_response", _consume_dialogue_response)
 	_router.register("save_result", _consume_save_result)
+	_router.register("debug_response", _consume_debug_response)
+
+	# #581: Wire settings_dialog debug console toggle → debug_console.set_enabled
+	if settings_dialog and debug_console:
+		settings_dialog.debug_console_toggled.connect(debug_console.set_enabled)
 
 
 func _process(delta: float) -> void:
@@ -382,6 +388,8 @@ func _consume_dialogue_response() -> void:
 	if GameState.dialogue_response == null or not dialogue_box:
 		return
 	var dr: Dictionary = GameState.dialogue_response
+	# v0.1: falls back to _last_dialogue_npc_id if wire omits speaker_entity_id.
+	# Edge case: fast re-engagement with a different NPC could misattribute — low probability.
 	var speaker_entity_id: int = dr.get("speaker_entity_id", _last_dialogue_npc_id)
 	var speaker_color_index: int = dr.get("speaker_color_index", -1)
 	var speaker_name: String = dr.get("speaker_name", _last_dialogue_npc_name)
@@ -414,6 +422,14 @@ func _consume_save_result() -> void:
 		monologue_display.show_notification(msg)
 
 
+# #581: Forward debug_response from server to the debug console.
+func _consume_debug_response() -> void:
+	if GameState.debug_response == null or not debug_console:
+		return
+	debug_console.append_response(GameState.debug_response)
+	GameState.debug_response = null
+
+
 # D-061: Handle dialogue option selection → send to server
 func _on_dialogue_option_selected(response_id: String, text: String) -> void:
 	SimBridge.send_input({