fix: generate litestream v0.5 retention config

[exKAZUu]

Customer Summary

• Restores the intended 3-day Litestream backup retention window for projects using the shared Docker setup.
• Keeps Litestream installation on the latest upstream release by default, while still allowing an explicit LITESTREAM_VERSION override when needed.
• Avoids Docker build failures from Debian architecture names that do not match Litestream release asset names.

Technical Summary

• Moves Litestream backup retention settings from the old replica-level v0.3 keys to the v0.5-compatible top-level snapshot.interval and snapshot.retention keys.
• Removes obsolete retention-check-interval generation because v0.5 enforces snapshot retention during snapshot compaction.
• Derives the default ARCH value as the Litestream release asset architecture (x86_64 or arm64) and uses it directly in the .deb filename.
• Preserves optional LITESTREAM_VERSION and ARCH overrides for callers that need them.

Why

• Production was running Litestream v0.5, but shared still generated v0.3-style retention keys, so the intended 72h retention was not applied.
• Using v0.5-compatible snapshot config makes the generated /etc/litestream.yml match the Litestream version currently installed by the Docker image.

Testing

• bash -n packages/wb/docker/bash/install-litestream.sh
• Verified latest Litestream release asset URLs for linux-arm64 and linux-x86_64 with curl -fsSI.
• Verified a generated v0.5-style snapshot: config is accepted by Litestream 0.5.12 via litestream databases -config.
• yarn verify
• Latest PR CI passed via bunx @willbooster-private/agentic-workflows@latest skills check-pr-ci.

[gemini-code-assist]

Code Review

This pull request pins the Litestream version in the installation script and refactors the Litestream configuration in the Prisma command to move snapshot settings to the top level. However, a critical issue was found in the installation script where the default version was set to 0.5.12, which is a LiteFS version rather than a Litestream version (the latest stable being 0.3.13). This mismatch will cause the Docker build to fail with a 404 error.

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