chore(release): let bump-version.sh file the bump's tracking issue #1226

Summary

scripts/bump-version.sh requires a tracking issue (--issue N, or a prompt that only accepts a number), so every bump starts with filing a near-identical chore(release): bump version to <v> issue by hand (#1117, #1134). The script already knows everything that issue needs: title, labels, milestone, and body.

Proposal

• With no --issue, pressing Enter at the issue prompt (or passing --yes) files the issue: title chore(release): bump version to <version>, labels chore, area:release, priority/p2, size/xs, the resolved milestone, assigned to @me.
• File it only after the final confirm, so answering "no" leaves nothing behind.
• Reuse an open issue with that exact title instead of filing a duplicate (a rerun after a failed run).
• Show the new issue in the confirm summary, and the gh issue create call under --dry-run.

Cross-surface impact

• core/llm/registry/tools/integrations: not affected
• TypeScript parity (planned): not affected, release tooling only
• CLI: not affected
• Nextra docs site: docs/releasing.md bump paragraph
• docs/verified-apis.md: not affected

Out of scope

• Changing the version menu or milestone resolution.

Done when

• bump-version.sh with no --issue files (or reuses) the tracking issue and names the branch after it.
• --dry-run shows the issue it would file and changes nothing.
• test_release_version.py still passes.