feat: obol wallet import — inject existing key into remote-signer

[bussyjd]

Problem

obol stack up always auto-generates a fresh wallet via GenerateWallet(). There's no way to inject an existing private key into the remote-signer. Users who already have funded wallets must manually transfer funds to the auto-generated address every time.

This came up during dual-stack testing: Bob's derived wallet (funded on Base Sepolia) is different from the remote-signer's auto-generated wallet. Every test run requires a manual USDC transfer.

Proposal

# Import an existing key into the remote-signer
obol wallet import --private-key-file /path/to/key

# Or during openclaw setup
obol openclaw setup --wallet-key-file /path/to/key

This would:

1. Convert the raw private key to a Web3 V3 keystore
2. Store it in the remote-signer keystores directory
3. Update wallet.json with the imported address
4. Restart the remote-signer to pick up the new key

Context

• Current: GenerateWallet() in internal/openclaw/wallet.go
• Remote-signer reads keystores from PVC at startup
• The key format is Web3 V3 JSON keystore (encrypted with a random password stored in values-remote-signer.yaml)