fix: refresh sibling release pull requests

[ThomasK33]

Summary

• create GitHub releases before creating or updating release PRs
• reload the release-please manifest after tagging so sibling release PRs are rebuilt on the new main
• add a regression test that locks in releases-first ordering

Why

The custom harness previously called createPullRequests() first. Immediately after one component release PR merged, release-please detected that merged PR as untagged and aborted, so the remaining component PRs stayed based on the old manifest and conflicted. The stock release-please action uses releases-first ordering.

Validation

• pnpm check
• pnpm --filter @coder/release-please-ai test:unit
• pnpm --filter @coder/release-please-ai typecheck
• live verification: reran release-please after agent 0.4.0 was tagged; sandbox chore(sandbox): release 0.3.0 #27 and provider chore(provider): release 0.3.0 #28 were force-refreshed from the new main and became mergeable

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