fix: prevent GitHub releases check from blocking app on API failure

[ajnart]

Summary

• Add optional fallbackToStaleOnError to the cached request handler so failed upstream fetches can return last-known-good Redis data instead of throwing
• Harden the update checker against GitHub API failures (401, quota exhausted, unreachable): disable Octokit throttling for fast failure, extend cache TTL to 24h, and enable stale fallback
• Reduce GitHub API pressure by running the update checker cron daily and respecting cache TTL instead of force-refreshing every hour

Closes #5786

Context

Users reported Homarr becoming completely inaccessible when the GitHub releases endpoint returns quota errors — especially visible in regions where GitHub is unreliable. The update checker was hitting GET /repos/homarr-labs/homarr/releases too often and Octokit would retry throttled requests, blocking admin page loads.

Test plan

• NODE_ENV=development pnpm exec vitest run packages/request-handler/src/test/update-checker.spec.ts
• Verify admin dashboard loads when GitHub API is unreachable (no update indicator shown, no page hang)
• Verify update indicator still appears when GitHub API is reachable and a newer release exists
• Verify stale cached update data is served when GitHub fails after a prior successful fetch

[Meierschlumpf]

This one seems of (119 files for a small bugfix should not be necessary). It seems like you have unrelated changes in this pr

[ajnart]

This one seems of (119 files for a small bugfix should not be necessary). It seems like you have unrelated changes in this pr

I'm very confused how it got this bad, I'll fix it asap