fix(build): improve asset download resilience against rate limits

[John-David Dalton (jdalton)]

Summary

• Increase GitHub release cache TTL from 1h to 4h to reduce API calls during repeated builds
• Use exponential backoff (factor 2) instead of linear retries for GitHub API requests
• Add SKIP_ASSET_DOWNLOAD env var to skip downloads when assets are already cached locally

The SKIP_ASSET_DOWNLOAD=1 toggle is useful when:

• Repeated local builds exhaust GitHub API rate limits
• Pre-commit hooks trigger rebuilds with cached assets
• Working offline with previously downloaded assets

Test plan

• Build succeeds with downloads
• All tests pass
• Test SKIP_ASSET_DOWNLOAD=1 pnpm build uses cached assets

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Note

Low Risk
Low risk build-infra behavior changes limited to caching/retry timings and an opt-in environment flag; main risk is stale release metadata for up to 4 hours or unintentionally skipping downloads when the env var is set.

Overview
Build asset fetching now makes fewer GitHub API calls by increasing the releases cache TTL from 1 hour to 4 hours.

GitHub API retries for release listing and asset URL lookup switch to exponential backoff (backoffFactor: 2, shorter base delay) to better handle rate limits.

The CLI asset downloader supports SKIP_ASSET_DOWNLOAD to bypass all downloads (useful for cached/offline builds).

^{Reviewed by Cursor Bugbot for commit 5241c44. Configure here.}