packages-to-build.R now saves the full (Package, Version) data.table
so the build step can pass specific tags to build_binary_package(),
eliminating redundant per-package tag discovery and S3 checks.
Also reduces archive versions from 9 to 4 (+ 1 release = 5 total).
The S3 credentials, endpoint, and bucket name were still pointing to the old Hetzner storage after the Backblaze migration, causing silent build failures.
