Support Assistent persona packs via git and local sync.

Replace assistent-personas overlay seed with assistent-extensions SFTP and an assistent: section in extensions.yaml so personalities install like other extensions without private URLs in the public repo.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/gpu_rent/payload.py

@@ -14,6 +14,9 @@ def is_skipped(path: Path) -> bool:
     name = path.name
     if name in SKIP_NAMES or name.startswith("."):
         return True
+    # Never sync git metadata (persona packs push shelves only).
+    if any(part == ".git" for part in path.parts):
+        return True
     return False