fix(delegation): backfill profiles.wallet_pubkey + document signer env — GHB-110

[aagear]

Fixes #110

Problem

On /app/credentials, clicking "Authorize" fails with Missing NEXT_PUBLIC_PRIVY_SIGNER_ID env var. Even when that env var is present, MCP submissions.create and whoami still fail with Profile has no wallet pubkey. because profiles.wallet_pubkey is never populated during delegation.

Changes

1. Backfill profiles.wallet_pubkey on delegate (agent-delegation-route-core.ts)

After the agent_delegations upsert succeeds, update profiles.wallet_pubkey where it is currently null. This is best-effort (failure doesn't block delegation) and never overwrites an existing value.

2. Document NEXT_PUBLIC_PRIVY_SIGNER_ID in .env.example

The env var was missing from .env.example entirely. Added with a comment explaining where to find the value in the Privy dashboard.

3. Improve client-side error message (AgentDelegationCard.tsx)

Old error gave no actionable guidance. New message points developers to frontend/.env.local and .env.example.

4. Tests (3 new + existing refactored)

• Verifies the profiles update call and payload
• Verifies .eq("user_id", ...) and .is("wallet_pubkey", null) scoping
• Verifies best-effort behavior (ok:true even if backfill fails)

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