feat: hpphub topup setup — one-command credit auto-top-up

[nolnol3]

Problem

Enabling x402 credit auto-top-up for the agent currently takes several manual
configuration steps. For users who are already logged in, it should be a single
command.

Proposal

Add hpphub topup setup to configure credit auto-top-up automatically:

• Wires up the integration from the user's existing login — no manual config editing.
• --enable-auto to opt into periodic automatic top-up.
• --dry-run to preview before applying.
• Safe to re-run (idempotent).

Any remaining one-time wallet steps are printed as guidance.

Acceptance

• hpphub topup setup configures auto-top-up with no manual file editing
• --enable-auto enables periodic top-up
• --dry-run previews without changes
• re-running is idempotent