bench 074: MEV-protect wallet RPC

[Flotapponnier]

New bench: wallet-method latency + method coverage across public MEV-protection gateways, keyless, 3 regions, 60s cadence (7 methods, 1.5s apart, polite by design).

• Providers: Flashbots Protect (rejects eth_call on the public endpoint, shown as a coverage gap), MEV Blocker (Consensys since Jan 2026, full set), Blink under slug blinklabs (full wallet set; the blink slug belongs to the unrelated HL frontend)
• Honesty framing baked into title, subtitle, methodology and FAQ: inclusion/refunds/sandwich efficacy are the write path, not measurable keyless; arXiv 2505.19708 cited as the one-off execution reference
• Harness smoke-tested locally: mevblocker 7/7 46ms, blinklabs 7/7 99ms, flashbots 6/7 112ms
• Prometheus scrape job added for mev-protect-{us,eu,sgp} (Railway services to create)
• /products/merkle 308 now points at /products/blinklabs (the successor page this bench creates)
• Logos: official blinklabs svg + mevblocker svg

64 specs valid, harness builds, tsc clean.