Limit CI builds to 2 cores to reduce RAM pressure

Kernel and qt5webengine builds are memory-intensive. Limiting to
2 parallel jobs prevents swapping on john-endesktop.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -59,7 +59,8 @@ jobs:
           for pkg in "${PACKAGES[@]}"; do
             echo "::group::Building $pkg"
             # Capture build output, extract store path (last line starting with /nix/store/)
-            if BUILD_OUTPUT=$(nix build ".#$pkg" --no-link --print-out-paths 2>&1); then
+            # --cores 2 limits parallel jobs to reduce RAM pressure on john-endesktop
+            if BUILD_OUTPUT=$(nix build ".#$pkg" --no-link --print-out-paths --cores 2 2>&1); then
               OUT_PATH=$(echo "$BUILD_OUTPUT" | grep '^/nix/store/' | tail -1)
               echo "$BUILD_OUTPUT"
               echo "Store path: $OUT_PATH"