feat(wallet): store P2PK signing keys and auto-sign on receive

[Forte11Cuba]

Description

Implements #1029. Adds persistent P2PK signing key storage to the CDK wallet using the existing KV store infrastructure.

When a user generates or stores a P2PK key, the private key is persisted in the wallet database. On receive, the wallet automatically looks up stored keys matching P2PK-locked proofs and signs them — no manual --signing-key argument needed.

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Notes to the reviewers

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Suggested CHANGELOG Updates

CHANGED

• Receive saga auto-loads stored P2PK keys and merges with manually provided keys (manual takes priority)

ADDED

• Store P2PK signing keys in wallet and auto-sign on token receive (Feature request cdk-wallet: store P2PK key and lookup automatically on token receive #1029)
• cdk-cli p2pk subcommand for key management (generate/store/list/remove)

REMOVED

FIXED

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Checklist

• I followed the code style guidelines
• I ran just final-check before committing

[thesimplekid]

We already have PR working on this #1466. Please give that a review if youre interested.