Add GPT-5 pricing for local Codex scans

[iam-brain]

Summary

• add GPT-5.4 and GPT-5.4 Pro pricing for local Codex scan data
• normalize GPT-5 snapshot and openai/-prefixed model names to the persisted scanner keys
• keep local-scan pricing on standard rates only, since persisted session JSONL does not include reliable priority/service-tier data

Validation

• pnpm check
• swift test --filter CostUsagePricingTests
• ./Scripts/compile_and_run.sh

Notes

• audited for scope containment and production readiness after the final pricing-data correction
• intentionally does not infer fast-mode pricing from model-name mentions or unpersisted runtime config