feat(products): add visibility controls

Summary

• Add product visibility as a persisted public/private attribute with migration, validation, seeds, and create/update support.
• Add a settings product detail page for editing name, description, visibility, and the linked GitHub repository.
• Show product visibility in the products table and use Noora select controls for product and spec dropdown fields.
• Let specs keep their own visibility override while still supporting inherited product visibility as a fallback.
• Polish specs table product badges so route CSS no longer overrides Noora badge internals.

Testing

• git diff --check
• mix compile --warnings-as-errors
• mix test

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