Reuse the repository directory by storing a state yaml

Not using the database for that so that removing the repository directory will
automatically recreate it

lib/git.py

@@ -181,6 +181,9 @@ class Git:
         except:
             return None
 
+    def branch_head(self, branch):
+        return self.repo.references["refs/heads/" + branch].target
+
     def gc(self):
         logging.info(f"Garbage recollec and repackage {self.path}")
         subprocess.run(