feat: bolt12 payments

[ye0man]

Summary

Add Bolt12 support as a first-class mint and melt payment method in
Coco.

Core is already structured around generic mint/melt method handlers,
so this should build on that architecture rather than introducing
Bolt12-specific one-off flows.

Goal

Support Bolt12 quote creation, tracking, execution, refresh/recovery,
and settlement for both:

• mint operations
• melt operations

Existing Bolt11 behavior should remain unchanged.

Model consideration

Bolt12 can allow quote ID reuse, so Coco should not assume that
(mintUrl, quoteId) uniquely identifies a single operation.

This likely means reviewing the current operation, history,
repository, and API surfaces that expose quote-based lookups.
Operation identity should remain operation-id based, while quote-based
lookup paths may need to support multiple operations or include enough
method/context to disambiguate.

Scope

• Core: add Bolt12 mint/melt method data, handlers, registration,
  validation, recovery, and quote-state handling.
• Persistence: ensure repositories and schema/index assumptions do not
  require quote IDs to be unique per mint when Bolt12 is used.
• React: expose Bolt12-capable mint/melt flows through the same
  operation APIs/hooks once core support exists.
• Tests: cover Bolt12 mint and melt flows, plus the quote-id reuse
  case.

Acceptance criteria

• Callers can initiate Bolt12 mint and melt operations through Coco’s
  generic operation APIs.
• Bolt11 remains compatible and unchanged.
• Multiple operations can safely reference the same Bolt12 quote ID
  without overwriting or confusing operation state.
• Persisted operations/history round-trip correctly when quote IDs are
  reused.