BC-250 console image: custom GNOME recipe with remote admin

Based on 62fixolab/Latest-Bazzite-AMD-BC-250-Patched-Images @ 347fd4d.

Adds on top of the fork:
- recipes/bc250-console-gnome.yml: governor + gnome-remote-desktop +
  openssh-server, sshd enabled, hhd.service masked, no signing module
  (local build + ISO path)
- files/console/usr/bin/bc250-remote-setup: one-time on-box SSH/RDP setup
- files/console/usr/lib/bootc/kargs.d/50-bc250-ttm.toml: ttm memory kargs
- BUILD-CONSOLE.md: build -> ISO -> validation instructions

files/console/ is separate from files/system/ so the 40-CU unlock tooling
stays out of this stable 24-CU image.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/prepare-build-matrices.py

@@ -0,0 +1,147 @@
+#!/usr/bin/env python3
+"""Prepare GitHub Actions matrices for changed Bazzite channel digests."""
+
+from __future__ import annotations
+
+import argparse
+import json
+import os
+from pathlib import Path
+
+
+NORMAL_RECIPES = {
+    "deck": ("bazzite-deck-patched.yml", "bazzite-bc250-patched-deck"),
+    "gnome": ("bazzite-gnome-patched.yml", "bazzite-bc250-patched-gnome"),
+    "kde": ("bazzite-kde-patched.yml", "bazzite-bc250-patched-kde"),
+}
+
+FORTYCU_RECIPES = {
+    "deck": ("bazzite-deck-patched-40cu.yml", "bazzite-bc250-patched-deck-40cu"),
+    "gnome": ("bazzite-gnome-patched-40cu.yml", "bazzite-bc250-patched-gnome-40cu"),
+    "kde": ("bazzite-kde-patched-40cu.yml", "bazzite-bc250-patched-kde-40cu"),
+}
+
+
+def read_digest_file(path: Path) -> dict[tuple[str, str], str]:
+    digests: dict[tuple[str, str], str] = {}
+    if not path.exists():
+        return digests
+
+    for raw_line in path.read_text(encoding="utf-8").splitlines():
+        line = raw_line.strip()
+        if not line:
+            continue
+
+        # Current format: channel<TAB>variant<TAB>base_image<TAB>digest
+        parts = line.split("\t")
+        if len(parts) >= 4:
+            channel, variant, _base_image, digest = parts[:4]
+            digests[(channel, variant)] = digest
+            continue
+
+        # Legacy stable cache format kept for migration from the previous workflow.
+        if "=" in line:
+            variant, digest = line.split("=", 1)
+            digests[("stable", variant)] = digest
+
+    return digests
+
+
+def read_current_entries(path: Path) -> list[dict[str, str]]:
+    entries: list[dict[str, str]] = []
+    for raw_line in path.read_text(encoding="utf-8").splitlines():
+        line = raw_line.strip()
+        if not line:
+            continue
+
+        parts = line.split("\t")
+        if len(parts) != 4:
+            raise SystemExit(f"Invalid current digest line: {raw_line}")
+
+        channel, variant, base_image, digest = parts
+        entries.append(
+            {
+                "channel": channel,
+                "variant": variant,
+                "base_image": base_image,
+                "base_digest": digest,
+            }
+        )
+
+    return entries
+
+
+def channel_package_name(base_name: str, channel: str) -> str:
+    if channel == "stable":
+        return base_name
+    return f"{base_name}-{channel}"
+
+
+def matrix_entry(entry: dict[str, str], recipe: str, base_package: str) -> dict[str, str]:
+    return {
+        **entry,
+        "recipe": recipe,
+        "image_name": channel_package_name(base_package, entry["channel"]),
+    }
+
+
+def github_output(values: dict[str, str]) -> None:
+    output_path = os.environ.get("GITHUB_OUTPUT")
+    if output_path:
+        with Path(output_path).open("a", encoding="utf-8") as handle:
+            for key, value in values.items():
+                handle.write(f"{key}={value}\n")
+    else:
+        for key, value in values.items():
+            print(f"{key}={value}")
+
+
+def parse_args() -> argparse.Namespace:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--current", required=True, type=Path)
+    parser.add_argument("--previous", type=Path)
+    parser.add_argument("--force", action="store_true")
+    return parser.parse_args()
+
+
+def main() -> int:
+    args = parse_args()
+
+    current_entries = read_current_entries(args.current)
+    previous = read_digest_file(args.previous) if args.previous else {}
+
+    normal: list[dict[str, str]] = []
+    fortycu: list[dict[str, str]] = []
+
+    for entry in current_entries:
+        key = (entry["channel"], entry["variant"])
+        previous_digest = previous.get(key)
+        if not args.force and previous_digest == entry["base_digest"]:
+            continue
+
+        variant = entry["variant"]
+        normal_recipe, normal_package = NORMAL_RECIPES[variant]
+        fortycu_recipe, fortycu_package = FORTYCU_RECIPES[variant]
+
+        normal.append(matrix_entry(entry, normal_recipe, normal_package))
+        fortycu.append(matrix_entry(entry, fortycu_recipe, fortycu_package))
+
+    normal_matrix = {"include": normal}
+    fortycu_matrix = {"include": fortycu}
+    total_count = len(normal) + len(fortycu)
+
+    github_output(
+        {
+            "normal-matrix": json.dumps(normal_matrix, separators=(",", ":")),
+            "normal-count": str(len(normal)),
+            "fortycu-matrix": json.dumps(fortycu_matrix, separators=(",", ":")),
+            "fortycu-count": str(len(fortycu)),
+            "should-build": "true" if total_count else "false",
+        }
+    )
+
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())