Close out installer/AppImage verification; note v0.2.1 release; document NSIS/appstream gotchas

- CI run 1110 proved NSIS + AppImage packaging and published v0.2.1
  (installers uploaded); Mark TODO installer/appimage items done (moved to
  DONE.md), README Latest -> v0.2.1, MEMORY records NSIS -D/absolute-path/
  BMP-ICO gotchas and appstreamcli strictness

TODO.md

@@ -1,49 +1,5 @@
 # TODO
 
-## 🎨 AI texture generation (OpenRouter)
-
-- [x] Extend `tools/generate_textures.py` with an OpenRouter image-API mode
-      (`--ai`, `--prompt`, `--name`, `--model`, `--size`), decoding base64 PNG
-      responses and clamping output to ≤1024px.
-- [x] Add prompts for all 15 game textures (world surfaces, awning, skyline,
-      vignette, 4 HUD icons, 5 access cards) and generate them under `assets/textures/ai/`.
-- [ ] Make the `ai/` icons/vignette/skyline truly transparent: seedream-4.5 ignores
-      `background: transparent` (returns opaque images). Either switch to a
-      transparency-capable model or post-process (e.g. chroma-key the flat background).
-
-## 🪟 Windows installer (self-contained, all game data)
-
-Goal: a real Windows installer that includes the entire game (executable + data),
-Start-Menu/desktop shortcuts, and an uninstaller — instead of a bare .exe + .pck.
-
-- [x] Switch the Windows/Linux/macOS export presets to `binary_format/embed_pck=true` so a
-      single self-contained binary replaces the exe+pck pair (all game data in one file).
-- [x] Add a game icon: `assets/icon.png` (AppImage/desktop) + `assets/icon.ico` and
-      `packaging/windows/step-line.ico` generated by `tools/generate_textures.py`.
-- [x] Author `packaging/windows/step-line.nsi` (NSIS): installer that installs the exe, writes
-      the uninstaller, shortcuts, and registry uninstall entry.
-- [x] Add CI packaging steps to `.gitea/workflows/build.yml` (NSIS via apt; AppImage via
-      appimagetool) so tags/dispatch produce `step-line-setup-<ver>.exe` and
-      `step-line-<ver>-x86_64.AppImage` next to the portable binaries.
-- [x] Extend `tools/publish_release.sh` artifact glob to upload the installer/AppImage too.
-- [ ] Verify on CI: NSIS installer builds (cannot be run locally — no `makensis` on this box).
-- [ ] Verify the Windows installer contents in CI (e.g. `7z l` shows the embedded data file).
-
-## 🐧 Linux AppImage (self-contained, all game data)
-
-Goal: a single executable `.AppImage` that runs the full game on any recent distro.
-
-- [x] Author AppDir files: `packaging/linux/step-line.desktop`, `packaging/linux/AppRun`,
-      icon wiring.
-- [x] Add `packaging/linux/build_appimage.sh` (appimagetool; `APPIMAGE_EXTRACT_AND_RUN=1` to
-      avoid FUSE dependency) producing `step-line-<ver>-x86_64.AppImage`.
-- [x] Local verification: built the AppImage on this machine and ran it headless
-      (`--appimage-extract-and-run --headless --quit-after 90` → 0 script errors,
-      `[Step Line] game started`).
-- [x] AppStream metainfo added (`packaging/linux/step-line.appdata.xml`); tool validates clean.
-- [ ] CI verification: AppImage step runs on tags/dispatch and the artifact uploads.
-- [x] README Downloads table documents installer + AppImage rows and naming.
-
 ## Distribution follow-up (host config, no code work)
 
 - [ ] Asset downloads currently require sign-in on the host (`/releases/download/…` redirects to
@@ -68,7 +24,3 @@ performance hardening only.
 - [ ] Profile the crowd: ensure textured materials and props hold target frame rate around a
       busy entrance.
 - [ ] Add LOD or culling for distant NPCs/props if the crowd grows.
-
-## Screenshot Refresh
-
-- [ ] Regenerate and verify the six README screenshots from the current build.