feat(ui): add diegetic time display on insert HUD (#263)

Time display on InsertOverlay (CanvasLayer 10) shows station local
time (HH:MM), day phase with cycle-tinted color, and day number.
Reads SimulationTime from GameState.game_time via update_from_state().
Adds Constants.format_game_time() helper for testability.
Placeholder layout — position refines when #314 wireframe lands.

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

client/scripts/main.gd

@@ -14,6 +14,7 @@ extends Node2D
 @onready var cursor_renderer = $UILayer/CursorRenderer  # D-056: z-layer 7
 @onready var gauntlet_hud = $UILayer/GauntletHUD  # #496: room timer + personal bests
 @onready var checklist_overlay = $UILayer/ChecklistOverlay  # #503: auto-checklist progress
+@onready var time_display = $InsertOverlay/TimeDisplay  # #263: diegetic time display (D-013, D-031)
 @onready var debug_overlay = $UILayer/DebugOverlay  # #511: F3 debug overlay
 @onready var bug_report_dialog = $ModalLayer/BugReportDialog  # #495: F12 WRONG button
 @onready var settings_dialog = $ModalLayer/SettingsDialog     # #528: audio settings (ESC/OPEN_MENU)
@@ -131,6 +132,10 @@ func _process(delta: float) -> void:
 		if checklist_overlay and checklist_overlay.has_method("update_from_state"):
 			checklist_overlay.update_from_state()
 
+		# #263: Update time display (D-013, D-031)
+		if time_display and time_display.has_method("update_from_state"):
+			time_display.update_from_state()
+
 		# #511: Update debug overlay (F3 toggle, dev tool)
 		if debug_overlay and debug_overlay.has_method("update_from_state"):
 			debug_overlay.update_from_state()