Adds a metrics HTTP server to acb-worker exposing Prometheus text format
at /metrics, plus /health and /ready K8s probe endpoints. Tracks counters
(matches, errors, jobs, replays, polls, heartbeats) and histograms
(match duration, replay upload duration, replay size). Instruments the
full worker execution flow. Fixes .gitignore binary patterns to use
root-anchored paths so cmd/ subdirectories aren't incorrectly excluded.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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