Implement GitHub caching with TanStack Query

[stylessh]

• Adds TanStack Query integration for dashboard routes with SSR hydration, browser cache persistence, typed GitHub query options, and preloaded Overview, Pull Requests, Issues, and Reviews routes.
• Introduces a D1-backed github_response_cache migration plus cached GitHub server functions with conditional revalidation, lower-concurrency fan-out, and cache behavior tests.
• Moves auth and GitHub worker access behind server-only modules and client-only auth actions to fix import-protection and cloudflare:workers leaks in the app graph.
• Updates related app config and generated artifacts, including Biome exclusions for worker types, route tree output, lockfile, and the turbo UI setting removal.
• Validation: pnpm --filter @quickhub/dashboard check-types and pnpm --filter @quickhub/dashboard test pass.