Add state.retention option to prevent big state buckets

[vimtor]

Summary

• add state.retention to keep the latest completed state snapshots
• prune matching snapshot, event log, update, and summary history across AWS, Cloudflare, and local homes
• permanently remove pruned S3 versions while preserving current state, secrets, and retained snapshots

Behavior

state: {
  retention: 30
}

Retention counts completed updates, not days. Omitted retention keeps all history. Pruning runs after an update and failures are non-fatal.

On AWS, retained snapshots become recovery history; noncurrent app checkpoints and stale lock versions are removed. On Cloudflare R2 and local homes, stale history objects are deleted explicitly.

Tests

• bun run test:cli
• go test ./pkg/project/...
• bun run typecheck
• bun run build:cli
• git diff --check

bun run build:platform completed TypeScript bundling, but local Docker reported that its driver does not support multi-platform builds; command exited 0.

Supersedes #6669.

[mclean25]

@vimtor just finished deploying to my test stage I've been using for a long time and it seems to have worked quite well. I got Codex to summarize the before/after and logs in case any of this is useful for you: