Broaden codex-usage positioning beyond per-machine attribution

[zJay26]

Summary

• position codex-usage as local-first Codex usage analytics while retaining per-machine attribution as the signature hook
• explain model/token-category, project, Thread/Session, Agent, local-day, API-equivalent-cost, pricing-coverage, and data-quality views
• clarify that codex-usage complements official account-level /usage rather than replacing it
• refresh Dashboard metadata, bilingual v1.0.0 notes, and the 1280×640 Social Preview

Boundaries

• no accounting, collection, SQLite, JSON/CSV, or /api/v1/* behavior changed
• equivalent cost remains an estimate, not account quota or a real bill
• no personal GitHub profile changes

Validation

• go test ./...
• go vet ./...
• npm test — 9/9 Playwright tests passed
• Social Preview verified at 1280×640; changed text passed path/UUID sensitive-pattern scan