[codex] Add towncrier to release extra

[adamtheturtle]

Summary

Add towncrier==25.8.0 to the release extra so the release workflow can run:

uv run --extra=release towncrier build ...

The previous towncrier migration added the tool for development/docs builds, but release jobs install only the release extra before invoking towncrier.

Validation

• uv lock
• uv run --no-dev --extra=release towncrier --version
• repo pre-commit / pre-push hooks run by git commit and git push

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Note

Low Risk
Low risk dependency metadata change; it only affects what gets installed when using the release extra and does not touch runtime code paths.

Overview
Ensures release environments can run towncrier by adding towncrier==25.8.0 to the release optional dependency extra in pyproject.toml (alongside check-wheel-contents).

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