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/start_menu.gd

@@ -0,0 +1,140 @@
+class_name StartMenu
+extends CanvasLayer
+## Startup menu: pick a venue, start the shift, open settings, or quit.
+## Keyboard and mouse both work. Replaces `V` as the player-facing venue path
+## (the `V` bind stays as a debug shortcut).
+
+signal venue_selected(scenario_id: String)
+signal settings_requested()
+signal quit_requested()
+
+const VENUES := [
+	{"id": "hollywood_building", "label": "Hollywood Boulevard", "blurb": "Building entrance, tourists and late-night trouble."},
+	{"id": "joke_shop", "label": "The Joke Shop", "blurb": "Guest list, IDs and wand screening."},
+	{"id": "tv_studio", "label": "Late Night TV Studio", "blurb": "Credentials, filming boundary, celebrity arrivals."},
+]
+
+var _index := 0
+var _buttons: Array[Button] = []
+var _root: Control = null
+
+func _ready() -> void:
+	layer = 20
+	_build()
+	hide()
+
+func _build() -> void:
+	_root = Control.new()
+	_root.name = "StartMenuRoot"
+	_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(0.03, 0.04, 0.07, 0.96)
+	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.name = "Column"
+	column.custom_minimum_size = Vector2(460, 0)
+	column.add_theme_constant_override("separation", 14)
+	center.add_child(column)
+
+	var title := Label.new()
+	title.text = "STEP LINE"
+	title.add_theme_font_size_override("font_size", 44)
+	title.horizontal_alignment = HORIZONTAL_ALIGNMENT_CENTER
+	column.add_child(title)
+
+	var subtitle := Label.new()
+	subtitle.text = "Pick a venue to start your shift."
+	subtitle.horizontal_alignment = HORIZONTAL_ALIGNMENT_CENTER
+	subtitle.add_theme_color_override("font_color", Color(0.72, 0.75, 0.82))
+	column.add_child(subtitle)
+
+	for i in VENUES.size():
+		var venue: Dictionary = VENUES[i]
+		var button := Button.new()
+		button.name = "Venue_%s" % venue["id"]
+		button.text = "%s\n%s" % [venue["label"], venue["blurb"]]
+		button.alignment = HORIZONTAL_ALIGNMENT_LEFT
+		button.custom_minimum_size = Vector2(460, 62)
+		button.pressed.connect(_on_venue_pressed.bind(i))
+		column.add_child(button)
+		_buttons.append(button)
+
+	var spacer := Control.new()
+	spacer.custom_minimum_size = Vector2(0, 10)
+	column.add_child(spacer)
+
+	var row := HBoxContainer.new()
+	row.alignment = BoxContainer.ALIGNMENT_CENTER
+	row.add_theme_constant_override("separation", 12)
+	column.add_child(row)
+
+	var settings_button := Button.new()
+	settings_button.name = "SettingsButton"
+	settings_button.text = "Settings"
+	settings_button.pressed.connect(func(): settings_requested.emit())
+	row.add_child(settings_button)
+
+	var quit_button := Button.new()
+	quit_button.name = "QuitButton"
+	quit_button.text = "Quit"
+	quit_button.pressed.connect(func(): quit_requested.emit())
+	row.add_child(quit_button)
+
+	var hint := Label.new()
+	hint.text = "Up/Down to choose, Enter to start, Esc to quit"
+	hint.horizontal_alignment = HORIZONTAL_ALIGNMENT_CENTER
+	hint.add_theme_color_override("font_color", Color(0.55, 0.58, 0.65))
+	column.add_child(hint)
+
+	_focus_index(0)
+
+func _focus_index(i: int) -> void:
+	if _buttons.is_empty():
+		return
+	_index = clampi(i, 0, _buttons.size() - 1)
+	_buttons[_index].grab_focus()
+
+func open() -> void:
+	visible = true
+	_root.visible = true
+	Input.set_mouse_mode(Input.MOUSE_MODE_VISIBLE)
+	_focus_index(_index)
+
+func close() -> void:
+	visible = false
+	_root.visible = false
+
+func _unhandled_input(event: InputEvent) -> void:
+	if not visible:
+		return
+	if event is InputEventKey and event.pressed and not event.echo:
+		match event.keycode:
+			KEY_UP, KEY_W:
+				_focus_index(_index - 1)
+				get_viewport().set_input_as_handled()
+			KEY_DOWN, KEY_S:
+				_focus_index(_index + 1)
+				get_viewport().set_input_as_handled()
+			KEY_ENTER, KEY_KP_ENTER, KEY_SPACE:
+				_on_venue_pressed(_index)
+				get_viewport().set_input_as_handled()
+			KEY_ESCAPE:
+				quit_requested.emit()
+				get_viewport().set_input_as_handled()
+
+func _on_venue_pressed(i: int) -> void:
+	if i < 0 or i >= VENUES.size():
+		return
+	var venue: Dictionary = VENUES[i]
+	close()
+	venue_selected.emit(str(venue["id"]))