Refresh pricing dynamically from GitHub Docs

[devartifex]

Summary

• automatically refresh stale pricing from GitHub Docs before rendering or starting the dashboard
• preserve last-known-good pricing on failures, retry with backoff, and write cache updates atomically
• parse current providers, fast model variants, and long-context pricing thresholds correctly
• add regression coverage for Anthropic cache-creation billing from Cost double-counts cache_creation tokens (billed at both input and cache_write rates) for Anthropic models #6
• include the Vitest/Vite updates from Bump the npm_and_yarn group across 1 directory with 2 updates #8

Closes #6
Supersedes #8