* add usage info to branch summary entries
* add usage to compaction entries
* allow custom tools to report llm usage in tool results
* allow observing and patching usage in tool_result hooks
* agent-harness: save usage in entries
for compaction, branch summaries and tool results
Move provider auth and OAuth flows onto pi-ai Models, compose models.json and extension overlays through ModelRuntime, and retain ModelRegistry as an extension compatibility facade.
Use visibleWidth/truncateToWidth for footer path and stats truncation so wide Unicode text cannot overflow terminal width.
Add regression tests for wide session/model/provider names and document the fix in changelog.
closes#1833
David Brailovsky