cost service: add platform base + per-VIN resource model with CPU/RAM display
- Updated cost model to show: (Platform Base) + (Per-VIN × VINs)
- Platform base: 176 cores / 896GB RAM (Kafka, ClickHouse, MongoDB, Redis, PostgreSQL, gateway, monitoring)
- Per-VIN marginal: 50mc / 82MB per vehicle
- Added RESOURCE USAGE MODEL and COST FORMULA sections to report
- Added CPU (mc) and RAM (MB) columns to TOP COST VEHICLES table
- Updated README with new report output
- virtual-vehicle: documented Vault cert TTL error troubleshooting
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