Moves stage_spinner() from a private function in sync.rs to a pub function
in cli/progress.rs so it can be reused by the timeline and search commands.
The function creates a numbered spinner (e.g. [1/3]) for pipeline stages,
returning a hidden no-op bar in robot mode to keep caller code path-uniform.
sync.rs now imports from crate::cli::progress::stage_spinner instead of
defining its own copy. Adds unit tests for robot mode (hidden bar), human
mode (prefix/message properties), and prefix formatting.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>