fix: query all Square locations for Lightning payment lookups

[gudnuf]

Summary

• Fetch all active Square locations at startup via GET /v2/locations
• Iterate over each location when checking for Lightning payments during melt validation
• Fixes merchants with multiple locations (e.g. Pink Owl Coffee with 5 locations) where Lightning payments happen at a non-default location and are missed by the single-location query

Changes

• types.rs — Added ListLocationsResponse and SquareLocation types
• square_api.rs — Added list_locations(), added location_id param to list_payments(), updated has_lightning_payment_near_timestamp() and log_recent_lightning_payments() to iterate all locations
• lib.rs (cdk-agicash) — Added location_ids field to ClosedLoopValidator::Square, threaded through validation
• lib.rs (cdk-mintd) — Fetch locations at startup, pass to ClosedLoopPayment::new_square()

Test plan

• cargo check -p cdk-agicash passes
• cargo check -p cdk-mintd passes
• cargo test -p cdk-agicash passes
• Rebuild cdk-mintd image, deploy to prod
• Verify startup log: "Discovered N active Square location(s)"
• Test melt at Pink Owl — should find Lightning payments at non-default location