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/test/smoke_focus_radial.gd

@@ -15,12 +15,23 @@ var state := 0
 var state_frames := 0
 var stage_npc: Node3D = null
 var failures: Array[String] = []
+var _shift_started := false
 
 func _initialize() -> void:
 	root.size = Vector2i(1280, 720)
 	var packed: PackedScene = load("res://scenes/main.tscn")
 	root.add_child(packed.instantiate())
 
+## The game now boots into the venue menu, so the smoke starts a shift first.
+func _start_shift_if_needed() -> void:
+	if _shift_started or gm == null:
+		return
+	var menu = gm.get("start_menu")
+	if menu != null and menu.visible:
+		gm.call("_on_venue_selected", "hollywood_building")
+		_shift_started = true
+		print("smoke: started hollywood_building shift from the menu")
+
 func _process(_delta: float) -> bool:
 	frames += 1
 	if gm == null:
@@ -39,6 +50,7 @@ func _advance() -> void:
 	state_frames += 1
 	match state:
 		0:
+			_start_shift_if_needed()
 			# Wait for the guard to settle on the ground, then grab one NPC.
 			if state_frames >= 40 and gm.npcs.size() > 0:
 				print("smoke: spawn guard_y=%.2f z=%.2f" % [