fix(tempo): bind proof signatures to realm + wallet (EIP-712 v2)

[stevencartavia]

Zero-amount Tempo proofs weren't bound to the realm, allowing cross-realm replay. Aligns the proof EIP-712 ABI with the canonical SDKs (mpp-rs, mppx).

• domain version "1" → "2"
• Proof(string challengeId) → Proof(string challengeId,string realm)
• client signs / server verifies with the challenge realm
• wallet binding unchanged (signer recovered & compared to the did:pkh source)
• adds test_proof.rb

Note: breaking for old v1 proofs

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