Adds _RollingCounter and _StatsCollector to the tracker: three rolling windows
(hour=60×1min, day=24×1hr, month=30×1day) track request RPMs per model.
GET /v1/stats returns combined local + peer stats. POST /v1/stats/gossip lets
trackers push their local slice for additive merge in hive mode.
SQLite persistence via --stats-db flag; stats survive tracker restarts.
Records a stat for each proxied /v1/chat/completions request.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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