Description

• Fix the Hydrogen Context Setup example in skills/sanity-best-practices/references/hydrogen.md by initializing a single previewSession before it is used.
• Reuse that same previewSession in both isPreviewEnabled(...) and preview.session so the example is internally consistent.
• Fix the loader example in the same file to use the destructured sanity variable directly when calling query(...), while still passing params and returning initial.

What to review

• Review skills/sanity-best-practices/references/hydrogen.md only.
• In the Context Setup example, confirm previewSession is initialized once before createSanityContext(...) and reused for both the stega.enabled check and preview.session.
• In the loader example, confirm the destructured sanity binding now matches the sanity.query(PRODUCT_QUERY, params) call and the example still returns {initial}.

Testing

• No automated tests were added because this PR only updates documentation examples.
• Validated manually by reviewing the updated snippets against the current code in hydrogen.md to confirm both findings were still valid, the fixes are minimal, and the examples remain internally consistent.