chore: fix turbo cache configuration in ci

Your workflows set TURBO_CACHE: remote:rw, which disables Turborepo's local cache. Since remote:rw omits the local: source, Turborepo never writes to .turbo/cache, the directory is never created, and actions/cache has nothing to save.

This is a pre-existing issue that StarSling has identified - the .turbo directory was a stale ~68 MB artifact restored from GHES cache (never regenerated by turbo build), and the Post Cache turbo build setup silently failed every time with Unable to reserve cache with key.

Fix

Remove TURBO_CACHE: remote:rw and let it default to local:rw,remote:rw. This is what Turborepo's GitHub Actions guide recommends — both local and remote caching active, with actions/cache persisting .turbo across CI runs. Your remote cache (84% hit rate, 2,445/2,900 lookups) continues working as before; the local cache adds a faster first-check layer.

Changes

• .github/workflows/ci.yml
• .github/workflows/e2e.yml
• .github/workflows/preview.yml

References

• Turborepo --cache flag — TURBO_CACHE syntax; omitting local: disables local reads and writes
• Turborepo: GitHub Actions Guide — recommended actions/cache setup with local + remote caching
• Turborepo: Constructing CI — remote caching as primary CI strategy
• Turborepo: Caching — .turbo/cache as default local cache directory (v2+)
• vercel/turborepo#842 — cache directory moved from node_modules/.cache/turbo to .turbo/cache in v2

Summary by cubic

Enable Turborepo local caching in CI by removing TURBO_CACHE=remote:rw, so actions/cache can save .turbo and reduce build times. Remote caching remains active.

• Bug Fixes
  • Fixed CI cache failures where .turbo/cache was never created, causing "Unable to reserve cache" on post-save.

^{Written for commit 3dd0932. Summary will update on new commits.}