Enable nutrition log creation and update write scopes

[marcelmarais]

Summary

• expose the supported create operation for nutrition-log
• mark nutrition-log as writable and document the operation
• update the six renamed OAuth write scopes to their current .writeonly names

Why

The Google Health API create endpoint accepts nutrition-log data with the nutrition.writeonly scope, but the CLI registry currently hides create for that type. The API also renamed its write scopes in the May 26 release, while the CLI still requests the previous names.

This lets agents and users run ghealth data nutrition-log create with a JSON payload after authorizing the nutrition write scope.

Fixes #6.

Validation

• go test ./...
• verified the generated dry-run request uses POST /v4/users/me/dataTypes/nutrition-log/dataPoints

[gemini-code-assist]

Caution

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[marcelmarais]

Closing this draft because I will maintain the change in my personal fork instead.