Merge branches (11 topics incl. balance-resume) into 6.18/testing
Also merges '6.18/topics/delayed-ref-fixes' (resume the delayed-ref merge walk instead of restarting it).
Also merges '6.18/topics/logical-ino' (added 2026-09-19: BTRFS_LOGICAL_INO_ARGS_COMMIT_ROOT, an opt-in commit-root walk so LOGICAL_INO callers stop pinning the tree mod log).