docs: lead the properties section with the check and add a Zod Mini tab

[colinhacks]

Since #6594 z.properties() is a check, but the API reference still led with z.instanceof().properties(), which Zod Mini doesn't have. The section now opens with the spread form both builds share, in a Zod / Zod Mini tab pair, and the method follows as the Zod-only sugar that narrows the inferred type.

Kept the method rather than dropping it, since the narrowing is the only thing it buys — .check() returns this in both builds, so the spread form infers plain Response. Also moved the no-clone fact up into the Instanceof intro and stated it directly: parsing returns the exact object that was passed in, which covers every instance schema rather than just the properties check.

Refs #6594

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[pullfrog]

✅ No new issues found.

Reviewed changes This review covers the API-reference update for z.instanceof() properties after z.properties() returned to its check role.

• Shared properties example Documents the iterable z.properties() check with equivalent Zod and Zod Mini examples, while retaining classic .properties() as narrowing sugar.
• Instance identity Moves the in-place, identity-preserving parsing behavior to the z.instanceof() introduction and illustrates it directly.

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