signMessage drops the COSE_Key, producing an incomplete CIP-30 DataSignature

## Summary
CIP-30 `signData` returns a `DataSignature` of `{ signature, key }`, where `key` is the CBOR-encoded COSE_Key needed to verify the signature. `SignData.signData` produces both, but the wallet's `signMessage` returns only `{ payload, signature }` and drops the key, and the `SignedMessage` interface has no `key` field. A consumer therefore cannot verify a message signed via the wallet API without obtaining the public key some other way, which breaks self-contained CIP-30 verification. No security impact: the dropped value is a public key, so nothing is leaked or made forgeable — it is a functional / spec-compliance gap.

## Affected
packages/evolution/src/sdk/client/internal/Signing.ts
- signMessage (L363-381): returns `{ payload, signature }` at L380, dropping `signed.key`

packages/evolution/src/sdk/wallet/Wallet.ts
- SignedMessage interface (L37-39): has payload + signature, no `key`

contrast: packages/evolution/src/cose/SignData.ts SignedMessage (L39-41) already carries `{ signature, key }`

## Fix
Add a `key` field to the wallet `SignedMessage` interface and return `Bytes.toHex(signed.key)` from `signMessage`. Ensure the CIP-30 api-wallet path carries the key through as well, so both wallet types return a complete DataSignature.

## Regression test
- given: a message signed via `wallet.signMessage`
- before fix: result has no `key` field; `verifyData` cannot be called without externally supplying the public key
- after fix: result includes the COSE_Key hex, and `verifyData(address, keyHash, payload, { signature, key })` verifies
Must FAIL on main today and PASS after the fix.

## Reference
Reported informally (signMessage drops COSE_Key). Standard basis: CIP-30 DataSignature = `{ signature, key }`.

Read packages/evolution/src/sdk/client/internal/Signing.ts signMessage and packages/evolution/src/sdk/wallet/Wallet.ts SignedMessage, then compare them with packages/evolution/src/cose/SignData.ts. Add a regression test for wallet.signMessage and verifyData: the returned result should include the COSE_Key and verification should succeed for both wallet API paths.

索引モデルが issue の本文から書いたものです。