docs: document real sandbox wallet signatures

[DhruvPareek]

Summary

• Document sandbox signed wallet actions using the decrypted session signing key and a Turnkey API-key stamp over the exact payloadToSign.
• Explain that sandbox validates the P-256 stamp and requires the signing public key to belong to an active sandbox wallet session.
• Update the scripts README sandbox tip while keeping the legacy sandbox-valid-signature compatibility path documented.

Testing

• Not run separately; this branch only changes MDX/README prose. The lower docs PR ran npm run build:openapi and npm run lint:openapi.

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Project	Deployment	Actions	Updated (UTC)
grid-flow-builder	Ready	Preview, Comment	May 23, 2026 12:13am

[DhruvPareek]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• docs: document real sandbox wallet signatures #494 👈 (View in Graphite)
• docs: document realistic sandbox passkeys #492
• docs: add sandbox email OTP inbox endpoint #489
• docs: explain realistic OIDC sandbox tokens #487 : 1 other dependent PR (#488 )
• main

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