feat: suggest systems by short name

--system gba, psx or ps1 was refused with no suggestion on RetroArch.
Short names now suggest the ids they stand for, never taken in their
place, and two aliases of one system name it once. --platform muos and
the other systems --list-platforms names stand for the file list they
get, and the run says which.

install.py

@@ -2236,15 +2236,58 @@ def _name_key(name: str) -> str:
 SHORT_LIST = 12
 
 
+# Names people type for a system, each with its id. Only ever suggested:
+# --system gba, psx and ps1 were refused with no hint on RetroArch, whose
+# list names no system that way, and taking one in silence could install
+# another console than the one meant.
+SYSTEM_SHORT_NAMES = {
+    **dict.fromkeys(("psx", "ps1", "ps", "playstation1"), "sony-playstation"),
+    "ps2": "sony-playstation-2", "ps3": "sony-playstation-3", "psp": "sony-psp",
+    **dict.fromkeys(("vita", "psvita"), "sony-playstation-vita"),
+    "gb": "nintendo-gb", "gbc": "nintendo-gbc", "gba": "nintendo-gba",
+    **dict.fromkeys(("nes", "famicom", "fc"), "nintendo-nes"), "fds": "nintendo-fds",
+    **dict.fromkeys(("snes", "sfc", "superfamicom"), "nintendo-snes"),
+    "n64": "nintendo-64", "n64dd": "nintendo-64dd", "sgb": "nintendo-sgb",
+    **dict.fromkeys(("nds", "ds"), "nintendo-ds"), "dsi": "nintendo-dsi",
+    "3ds": "nintendo-3ds", "wiiu": "nintendo-wii-u", "switch": "nintendo-switch",
+    **dict.fromkeys(("gc", "ngc", "gcn", "gamecube"), "nintendo-gamecube"),
+    "pokemini": "nintendo-pokemon-mini",
+    **dict.fromkeys(("md", "gen", "genesis", "megadrive"), "sega-mega-drive"),
+    **dict.fromkeys(("scd", "segacd", "megacd"), "sega-mega-cd"),
+    "32x": "sega-32x", **dict.fromkeys(("sms", "mastersystem"), "sega-master-system"),
+    **dict.fromkeys(("gg", "gamegear"), "sega-game-gear"),
+    **dict.fromkeys(("ss", "saturn"), "sega-saturn"),
+    **dict.fromkeys(("dc", "dreamcast"), "sega-dreamcast"),
+    **dict.fromkeys(("naomi", "atomiswave"), "sega-dreamcast-arcade"),
+    **dict.fromkeys(("pce", "tg16", "turbografx", "turbografx16", "pcengine",
+                     "supergrafx"), "nec-pc-engine"),
+    **dict.fromkeys(("pcecd", "tgcd", "turbografxcd"), "nec-pc-engine-cd"),
+    "pcfx": "nec-pc-fx",
+    **dict.fromkeys(("mvs", "aes"), "snk-neogeo"),
+    **dict.fromkeys(("neocd", "neogeocd"), "snk-neogeo-cd"),
+    **dict.fromkeys(("msx", "msx2"), "microsoft-msx"),
+    "c64": "commodore-c64", "c128": "commodore-c128",
+    **dict.fromkeys(("amiga", "cd32"), "commodore-amiga"),
+    "x68k": "sharp-x68000", **dict.fromkeys(("jag", "jaguar"), "atari-jaguar"),
+    **dict.fromkeys(("st", "atarist"), "atari-st"), "a800": "atari-400-800",
+    **dict.fromkeys(("coleco", "colecovision"), "coleco-colecovision"),
+    **dict.fromkeys(("intv", "intellivision"), "mattel-intellivision"),
+    "o2": "magnavox-odyssey2", "channelf": "fairchild-channel-f",
+    **dict.fromkeys(("zx", "spectrum", "zxspectrum"), "sinclair-zx-spectrum"),
+    "cpc": "amstrad-cpc", "bbc": "acorn-bbc-micro", "apple2": "apple-ii",
+}
+
+
 def did_you_mean(
     typed: list[str], known: list[str], listing: str,
-    aliases: dict[str, str] | None = None,
+    aliases: dict[str, str] | None = None, inside_from: int = 4,
 ) -> str:
     """The closest known names to what was typed, and the option listing them all.
 
     A typo was answered with every name the platform has, up to 400 on one
     line, with no hint that playstation is sony-playstation. An alias close
-    to what was typed suggests the name it stands for.
+    to what was typed suggests the name it stands for. A name holding what
+    was typed, inside_from letters or more, is suggested too.
     """
     import difflib  # noqa: PLC0415
 
@@ -2259,9 +2302,12 @@ def did_you_mean(
         if not key:
             continue
         matches = difflib.get_close_matches(key, list(by_key), n=3, cutoff=0.6)
-        if len(key) >= 4:
+        if len(key) >= inside_from:
             matches += sorted(k for k in by_key if key in k and k not in matches)
-        close += [by_key[k] for k in matches if by_key[k] not in close]
+        for k in matches:
+            # Two aliases of one system (psx, ps1) name it once.
+            if by_key[k] not in close:
+                close.append(by_key[k])
     if close:
         return f"Did you mean: {', '.join(close[:3])}? {listing} lists all {len(known)}."
     if len(known) <= SHORT_LIST:
@@ -2279,6 +2325,13 @@ def normalize_platform(name: str) -> str:
     for plat in AVAILABLE_PLATFORMS:
         if key and key in (_name_key(plat), _name_key(display_name(plat))):
             return plat
+    # --list-platforms prints `muOS: retroarch`, and --platform muos was
+    # refused: a system named there stands for the list it gets.
+    for rule in _EMBEDDED_RULES:
+        if key and rule.manifest and key == _name_key(rule.name):
+            print(f"  {rule.name} gets the {display_name(rule.manifest)} file list: "
+                  f"--platform {rule.manifest}.")
+            return rule.manifest
     print(f"Unknown platform '{name.strip()}'. "
           + did_you_mean([name], list(AVAILABLE_PLATFORMS), "--list-platforms"),
           file=sys.stderr)
@@ -3423,9 +3476,15 @@ def resolve_choices(
             raise ValueError(f"unknown {label}: {', '.join(unknown)}. This list records none.")
         listing = {"system": "--list-systems", "emulator": "--list-emulators"}.get(
             label, "--list-cores")
+        hints, inside_from = aliases, 4
+        if label == "system":
+            # gba is the end of nintendo-gba: three letters are enough here.
+            hints = {**{short: name for short, name in SYSTEM_SHORT_NAMES.items()
+                        if name in known}, **aliases}
+            inside_from = 3
         raise ValueError(
             f"unknown {label}: {', '.join(unknown)}. "
-            f"{did_you_mean(unknown, known, listing, aliases)}"
+            f"{did_you_mean(unknown, known, listing, hints, inside_from)}"
         )
     if values and not chosen:
         raise ValueError(f"--{label} needs at least one name")
@@ -7139,7 +7198,8 @@ def _install(args: argparse.Namespace, real_stdout: TextIO) -> None:
         print("Available platforms:")
         for p in AVAILABLE_PLATFORMS:
             print(f"  {p}")
-        print("\nSystems recognized by their own files:")
+        print("\nSystems recognized by their own files, and the file list each gets "
+              "(--platform takes either name):")
         for line in _system_lines():
             print(f"  {line}")
         detected = detect_platforms(os_type)