fix: mirror sync also skips local project name

Belt-and-suspenders: even if the manifest still contains a
self-reference to "stack", the sync script now filters it out
before building the pip download requirements list.

dev/scripts/pkg_mirror_sync.py

@@ -144,8 +144,12 @@ def _flat_apt_packages(manifest: dict) -> list[str]:
 def _flat_pypi_packages(manifest: dict) -> list[dict]:
     seen: set[str] = set()
     pkgs: list[dict] = []
+    # Skip the local project — it can't be downloaded from PyPI
+    local_project = "stack"
     for section in ("project_prod", "project_dev", "notebook", "dockerfile_adhoc"):
         for pkg in manifest.get("pypi", {}).get(section, []):
+            if pkg["name"] == local_project:
+                continue
             if pkg["name"] not in seen:
                 seen.add(pkg["name"])
                 pkgs.append(pkg)