feat: pm-fee-comparison and pm-geographic-access harnesses (live)

[Flotapponnier]

Summary

• New harness pm-fee-comparison: exposes pm_fee_taker_bps{venue} in basis points of $1 gross notional. Static for Polymarket (200bps flat 2%), Kalshi (700bps from published schedule), Manifold (0bps), Myriad (200bps). Limitless is live: polls /markets/active hourly, computes median half-spread across active USDC markets. Current reading: 490bps.
• New harness pm-geographic-access: HTTP probes each venue's market listing endpoint every 15min, publishes pm_geo_accessible{venue, region} = 1/0. Runs on VPS (eu-west). Can be deployed to Railway for us-east/sgp coverage. All 5 venues return 200 from EU West.
• Both specs updated from status: draft → status: live, with full rank_matrix_query and providers[].queries blocks.
• Both images built and running on VPS (ocb-pm-fee-comparison, ocb-pm-geographic-access). Prometheus scrape configs added.

Test plan

• Check pm-fee-comparison metrics: curl ocb-par-main:9090/api/v1/query?query=pm_fee_taker_bps
• Check pm-geographic-access metrics: curl ocb-par-main:9090/api/v1/query?query=pm_geo_accessible
• Verify bench pages load on staging after merge