ps1: embed real game art (ICON0 + PIC1) in converted EBOOTs

Fetch the game's cover art (libretro / ScreenScraper / IGDB / Wikipedia,
reusing the local cover cache) and bake it into the EBOOT's ICON0 (144x80
XMB icon) and PIC1 (480x272 launch background) instead of the default PS1
icon. Best-effort: falls back to the base icon/empty background when no art
is found. convert()/convert_to_folder() gain optional icon0/pic1 params.

README.md

@@ -202,6 +202,11 @@ PS1 discs (pending) and converted EBOOTs also show up in the **Library** tab
   compressed PSAR) plus a `KEYS.BIN` (NPDRM version key used to decrypt the
   `STARTDAT` PGD), ready to copy to `<PSP>/PSP/GAME/<Game ID>/`. Compatible
   with CFW POPS (ARK-4/ARK-5).
+- **Artwork** — the converter fetches the game's real cover art (libretro /
+  ScreenScraper / IGDB / Wikipedia, reusing the local cover cache) and bakes
+  it into the EBOOT's `ICON0` (144×80 XMB icon) and `PIC1` (480×272 launch
+  background), so the PSP shows the actual game rather than the default PS1
+  icon. Falls back to the base icon when no art is found.
 
 Configure the folders in **Settings → General** (or `PSP_PS1_ROOTS` /
 `PSP_PS1_OUTPUT_DIR`). Current limits: single-disc games only (no multi-disc