add db migration for improper NumberPool attributes on Templates

[ajtmccarty]

TODO:

• manual testing
• description

Why

Closes

What changed

How to review

How to test

# Commands to validate

Impact & rollout

• Backward compatibility:
• Performance:
• Config/env changes:
• Deployment notes:

Checklist

• Tests added/updated
• Changelog entry added (uv run towncrier create ...)
• External docs updated (if user-facing or ops-facing change)
• Internal .md docs updated (internal knowledge and AI code tools knowledge)

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[codspeed-hq]

Merging this PR will not alter performance

✅ 12 untouched benchmarks

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_{Comparing ajtm-02112026-template-number-pool-attr-migration (c3bced0) with develop (3cf38ce)}