nsats for manage and debit

[shocknet-justin]

Summary

• Debits: add info: true request shape returning spend allowance (policy + optional available_sats) — not wallet balance. Covers manual / budget / unrestricted relationships; info never prompts for approval. Payment ok responses SHOULD piggyback the same fields; clients that need freshness still poll.
• Manage: add offer action: "stats" with aggregates only (received_sats, paid_count) — no invoice history arrays.
• Manage clarifications: first resource action is the grant ask (no separate access request); grants are creator-scoped (not all user offers); wallet-native migration guidance (group/move by managing key; don’t widen list).