adjustments to npm publish workflow for OIDC publishing

[phryneas]

This PR makes changes to enable OIDC publishing to npm, so that we no longer need to use npm tokens stored in GitHub secrets.

It makes the following changes:

• Update the repository field in package.json files to the format that npm expects here - via npm pkg fix
• Add permissions required for OIDC publishing to the GitHub Actions workflow
• Ensures that the node version for publishing is node 24. npm versions shipping with older node versions cannot publish via OIDC. Some node 22 versions can, but it's a gamble and hard to debug if something goes wrong.
• Remove references to NPM_TOKEN secrets in the GitHub Actions workflow - or if using changesets, sets it to "" as changesets requires the env var to be set, but actually doesn't do anything - and it should be empty for OIDC publishing to work.

I have already gone ahead and set OIDC publishing on the npm side, so this is just the second half of the puzzle.

[changeset-bot]

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Latest commit: b7afb53

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