[core] Prevent tag deletion when referenced by branches

[ArnavBalyan]

Purpose

• A branch created from a tag shares the tag snapshot's data and manifest files. Deleting the tag makes the branch unqueryable.
• Block deleteTag with an error with referencing branches, so a tag cannot be removed while a branch depends on it.
• Make automatic tag expiration skip such tags with a warning instead, since it runs during commit and must not fail the commit.
• Supported for FileSystemBranchManager and CatalogBranchManager.

Tests

• UT

[JingsongLi]

After a branch is created from tag1, a branch-local tag1 is saved; after the main branch renames tag1 to tag2, branchesCreatedFromTag(“tag2”) cannot find the branch-local tag2, so deleteTag(“tag2”) can still be executed and delete the shared file, potentially making the branch unreadable again. Reference relationships cannot be determined based solely on tag names; at a minimum, renaming of referenced tags must be prevented, or associations must be persisted via snapshot or origin.