Add wallet/key management guidance for dApp use cases

[timfong888]

Problem

wallet init --auto stores a private key in config — correct for CLI/agent use, but dApps need user wallet connection (MetaMask, WalletConnect), not server-side keys.

Details

• privateKeyClient() in client.ts reads from config — no guidance for dApp wallet patterns
• human: I think maybe zooming out on how an agent can do this on behalf of the dApp and the limitations.
• Synapse React hooks (useAccountInfo, useUpload, useDeposit) exist but aren't referenced in skills
• Agents building dApps don't know whether to use the CLI wallet pattern or a browser wallet pattern

Ask

before implementation details, I think understanding what can or can't be done (I'm not clear myself) in terms of the dApp wallet set up (there will need to be human in the middle I think...)

Branch the skill/docs based on intent:

• Server-side / CLI / agent: current wallet init --auto flow (keep as-is)
• User-facing dApp: wallet connection via MetaMask/WalletConnect, Synapse React hooks, no server-side private key storage

This would help agents (and developers) pick the right wallet pattern for their use case.

[timfong888]

i have reviewed as a human.