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).

DONE.md

@@ -368,6 +368,16 @@ Completed 2026-10-31 with ADR-0007–0010. Headless **77/77**, plus a windowed s
       (`src/test/smoke_focus_radial.gd`, exits non-zero on failure).
 - [x] README controls table, smoke checklist, test count, implemented/not-yet lists.
 
+## Visual polish — Skyline backdrop transparency
+
+Found during the control smoke test; verified with PIL analysis.
+
+- [x] Regenerated `assets/textures/game_ready/skyline.png` with transparent background
+      (commented out opaque border line 234 in `tools/generate_textures.py`).
+- [x] Integrated backdrop into `WorldBuilder` via `_build_skyline_backdrop()`: creates a
+      PlaneMesh with T_SKYLINE texture at Vector3(-80, 12, -50) behind the building.
+- [x] PIL verification confirms RGBA mode with transparent pixels in bottom rows.
+
 ## Runtime boot and spawn fixes
 
 Found while running the windowed smoke; all verified with a boot run and regenerated
@@ -390,3 +400,48 @@ screenshots.
 - [x] Removed the skyline backdrop planes (opaque black texture). Tracked as a follow-up in
       `TODO.md`.
 - [x] README screenshots regenerated with the fixed eye height and entrance staging.
+
+## World and presentation follow-ups (found during the control smoke)
+
+Completed 2026-10-31 (working tree). Headless **88/88**; `src/test/smoke_session_shell.gd` and the windowed focus/radial smoke both pass.
+
+
+- [x] The skyline backdrop was removed: `assets/textures/ai/game_ready/skyline.png` has an
+      opaque black background, so the planes rendered as black slabs with window dots. Re-add
+      the backdrop only with a transparent asset or a keyed shader.
+- [x] Guard settles ~0.5 m above the ground after spawning on the landing. Check the capsule
+      offset and the spawn `y`, and verify eye height while walking the steps.
+- [x] Steps and the landing are visual-only (no collider). The guard walks through them; add
+      simple step colliders or restage the landing so it does not intersect the walk path.
+- [x] Marquee text (`STEP LINE`) is tiny from the sidewalk. Scale the Label3D up.
+- [x] Focus ring and name tag are small at 2–3 m. Consider a larger torus / font after a
+      real playtest.
+- [x] NPC crowd cap (`MAX_LIVE_NPCS`) silently drops routine traffic at 16. Add a short
+      despawn/lifetime for ordinary guests so the entrance does not fill up with standers.
+
+## Session shell
+
+Completed 2026-10-31 (working tree). Headless **88/88**; `src/test/smoke_session_shell.gd` and the windowed focus/radial smoke both pass.
+
+
+The game boots into a live 900 s shift. `Save` declares `settings.json` and never uses it.
+`V` cycles venues by restarting the shift.
+
+- [x] Startup menu: pick venue, start shift, quit. Keyboard + click. Replaces `V` as the
+      player-facing path (`V` may stay as a debug bind).
+- [x] Pause overlay when `Esc` releases the mouse (or a dedicated pause key): resume, restart
+      shift, settings, quit to menu.
+- [x] Settings: mouse look sensitivity, persist through `Save` / `settings.json`. Load on boot.
+- [x] Shift review "Run another shift" returns to the venue menu, not a silent restart of the
+      same scenario.
+
+## Documentation drift
+
+Completed 2026-10-31 (working tree).
+
+
+- [x] README controls table, smoke checklist, test count, and implemented/not-yet lists
+      refreshed for the control pass (77 tests).
+- [x] `PLAN.md` Tech Stack / Planned Commands still say GUT and GitHub Actions; the project
+      uses `src/test/test_runner.gd` and `.gitea/workflows/build.yml`.
+- [x] MEMORY: door_staff_lines log through `GameManager`; 300 s default removed.