fix(clerk-js): Backport iframe __client_uat cookie domain fix

[brkalow]

Summary

• Backport of fix(clerk-js): Prevent duplicate __client_uat cookies in iframe contexts #7875 to release/core-2
• Fixes __client_uat cookie being set on two different domain scopes when app is loaded in both iframe and non-iframe contexts
• getCookieDomain() now falls back to hostname instead of undefined when the eTLD+1 probe fails, and the probe uses the same SameSite/Secure attributes as the actual cookie

Test plan

• Verify existing getCookieDomain tests pass
• Verify __client_uat cookie is set correctly in iframe and non-iframe contexts

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🦋 Changeset detected

Latest commit: 27019fe

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@clerk/clerk-js	Patch
@clerk/chrome-extension	Patch
@clerk/clerk-expo	Patch

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Project	Deployment	Actions	Updated (UTC)
clerk-js-sandbox	Ready	Preview, Comment	Feb 18, 2026 8:58pm

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commit: 27019fe