Add session shell and close world presentation follow-ups

Session shell
- Startup venue menu (src/game/ui/start_menu.gd): keyboard + mouse, replaces
  the live-shift boot and V as the player-facing venue path (V stays a debug bind).
- Pause overlay on Esc (src/game/ui/pause_overlay.gd): resume, restart shift,
  settings, quit to menu.
- Settings panel (src/game/ui/settings_panel.gd): mouse look sensitivity and
  HUD font scale, persisted via Save into user://settings.json and loaded on boot.
- Shift review "Run another shift" now returns to the venue menu.
- New smoke: src/test/smoke_session_shell.gd (menu -> shift -> pause -> settings
  -> menu), passes headless and windowed.

World and presentation
- Skyline backdrop restored with a transparent asset and an alpha-scissor
  unshaded material; fixes the opaque black slab from the earlier attempt and
  the unimported texture path.
- Steps and landing are a StaticBody3D with per-tread colliders, so the guard
  and NPCs walk up instead of clipping through.
- Marquee Label3D scaled up (72 -> 160) so STEP LINE reads from the sidewalk.
- Focus torus and name tag enlarged for 2-3 m readability.
- Routine traffic despawns after an idle lifetime (NpcAvatar.ephemeral), so the
  16-NPC cap no longer fills with standers; authored events stay for the shift.

Docs and tests
- PLAN.md test/CI section corrected to the custom headless runner and Gitea Actions.
- README controls table, smoke checklist, test count, and status lists refreshed.
- TODO/DONE/MEMORY updated; completed sections moved to DONE.md.
- Headless suite 77 -> 88 passing (settings round-trip, step colliders, skyline
  alpha, session-shell UI behavior, traffic lifetime).

src/game/ui/settings_panel.gd

@@ -0,0 +1,154 @@
+class_name SettingsPanel
+extends CanvasLayer
+## Settings: mouse look sensitivity and HUD font scale, persisted through the
+## `Save` autoload into `user://settings.json`.
+##
+## Emits `applied(settings)` so the game manager can push values into the guard
+## and HUD as soon as the player confirms.
+
+signal applied(settings: Dictionary)
+signal closed()
+
+var _root: Control = null
+var _sensitivity: HSlider = null
+var _font_scale: HSlider = null
+var _sensitivity_value: Label = null
+var _font_scale_value: Label = null
+var settings: Dictionary = {}
+
+func _ready() -> void:
+	layer = 22
+	_build()
+	hide()
+
+func _init() -> void:
+	layer = 22
+	_build()
+	hide()
+
+func _build() -> void:
+	_root = Control.new()
+	_root.name = "SettingsRoot"
+	_root.set_anchors_preset(Control.PRESET_FULL_RECT)
+	_root.mouse_filter = Control.MOUSE_FILTER_STOP
+	add_child(_root)
+
+	var bg := ColorRect.new()
+	bg.color = Color(0.02, 0.03, 0.05, 0.9)
+	bg.set_anchors_preset(Control.PRESET_FULL_RECT)
+	bg.mouse_filter = Control.MOUSE_FILTER_IGNORE
+	_root.add_child(bg)
+
+	var center := CenterContainer.new()
+	center.set_anchors_preset(Control.PRESET_FULL_RECT)
+	_root.add_child(center)
+
+	var column := VBoxContainer.new()
+	column.custom_minimum_size = Vector2(420, 0)
+	column.add_theme_constant_override("separation", 12)
+	center.add_child(column)
+
+	var title := Label.new()
+	title.text = "Settings"
+	title.add_theme_font_size_override("font_size", 32)
+	title.horizontal_alignment = HORIZONTAL_ALIGNMENT_CENTER
+	column.add_child(title)
+
+	var sens_row := VBoxContainer.new()
+	column.add_child(sens_row)
+	_sensitivity_value = _add_label_row(sens_row, "Mouse look sensitivity")
+	_sensitivity = _add_slider(sens_row, 0.0005, 0.0060, 0.0001)
+	_sensitivity.value_changed.connect(_on_sensitivity_changed)
+
+	var font_row := VBoxContainer.new()
+	column.add_child(font_row)
+	_font_scale_value = _add_label_row(font_row, "HUD font scale")
+	_font_scale = _add_slider(font_row, 0.75, 1.75, 0.05)
+	_font_scale.value_changed.connect(_on_font_scale_changed)
+
+	var row := HBoxContainer.new()
+	row.alignment = BoxContainer.ALIGNMENT_CENTER
+	row.add_theme_constant_override("separation", 12)
+	column.add_child(row)
+
+	var save_button := Button.new()
+	save_button.name = "ApplyButton"
+	save_button.text = "Apply"
+	save_button.pressed.connect(_on_apply)
+	row.add_child(save_button)
+
+	var cancel_button := Button.new()
+	cancel_button.name = "CancelButton"
+	cancel_button.text = "Cancel"
+	cancel_button.pressed.connect(_on_cancel)
+	row.add_child(cancel_button)
+
+func _add_label_row(parent: Control, text: String) -> Label:
+	var row := HBoxContainer.new()
+	parent.add_child(row)
+	var label := Label.new()
+	label.text = text
+	label.size_flags_horizontal = Control.SIZE_EXPAND_FILL
+	row.add_child(label)
+	var value := Label.new()
+	value.add_theme_color_override("font_color", Color(0.75, 0.8, 0.9))
+	row.add_child(value)
+	return value
+
+func _add_slider(parent: Control, min_v: float, max_v: float, step: float) -> HSlider:
+	var slider := HSlider.new()
+	slider.min_value = min_v
+	slider.max_value = max_v
+	slider.step = step
+	slider.custom_minimum_size = Vector2(420, 24)
+	parent.add_child(slider)
+	return slider
+
+func open(current: Dictionary) -> void:
+	settings = current.duplicate(true)
+	var sens: float = float(settings.get("look_sensitivity", 0.0022))
+	var scale: float = float(settings.get("hud_font_scale", 1.0))
+	if _sensitivity:
+		_sensitivity.set_value_no_signal(clampf(sens, _sensitivity.min_value, _sensitivity.max_value))
+	if _font_scale:
+		_font_scale.set_value_no_signal(clampf(scale, _font_scale.min_value, _font_scale.max_value))
+	_sync_labels()
+	visible = true
+	_root.visible = true
+	Input.set_mouse_mode(Input.MOUSE_MODE_VISIBLE)
+
+func close() -> void:
+	visible = false
+	_root.visible = false
+
+func _sync_labels() -> void:
+	if _sensitivity_value and _sensitivity:
+		_sensitivity_value.text = "%.4f" % _sensitivity.value
+	if _font_scale_value and _font_scale:
+		_font_scale_value.text = "%.2fx" % _font_scale.value
+
+func _on_sensitivity_changed(value: float) -> void:
+	settings["look_sensitivity"] = value
+	_sync_labels()
+
+func _on_font_scale_changed(value: float) -> void:
+	settings["hud_font_scale"] = value
+	_sync_labels()
+
+func _on_apply() -> void:
+	if Save:
+		Save.save_settings(settings)
+	applied.emit(settings)
+	close()
+	closed.emit()
+
+func _on_cancel() -> void:
+	close()
+	closed.emit()
+
+func _unhandled_input(event: InputEvent) -> void:
+	if not visible:
+		return
+	if event is InputEventKey and event.pressed and not event.echo and event.keycode == KEY_ESCAPE:
+		_on_cancel()
+		get_viewport().set_input_as_handled()