cmd/git(fix[init]): Don't pass --shared when shared=False

why: Both shared=True and shared=False were passing --shared flag.
Per git-init docs, --shared without value defaults to group permissions.
shared=False should mean "no --shared flag", not default group sharing.
what:
- Only append --shared when shared is explicitly True
- shared=False now behaves like shared=None (no flag)

Author: tony

src/libvcs/cmd/git.py

@@ -1256,7 +1256,9 @@ def init(
                 "everybody",
             }
             if isinstance(shared, bool):
-                local_flags.append("--shared")
+                if shared:
+                    local_flags.append("--shared")
+                # shared=False means no --shared flag (same as None)
             else:
                 shared_str = str(shared).lower()
                 # Check if it's a valid string value or an octal number