Payback note recipient is built with SWAPP.masm instead of P2ID.masm

### Summary

`build_p2id_recipient()` is intended to build the recipient for the payback P2ID note created after a SWAPP note is consumed, but it currently loads `scripts/SWAPP.masm` instead of `scripts/P2ID.masm`.

### Why this matters

The resulting payback note recipient digest commits to the SWAPP script root while the note inputs are shaped like a P2ID note. That makes the payback note inconsistent: consuming it as a normal P2ID note will not match the committed script root, while consuming it with SWAPP logic expects the SWAPP input shape.

This affects the core CLOB example flow because the payback note is how proceeds are returned to the matched counterparty.

### Code path

`backend/order-book/src/note/mod.rs`:

```rust
fn build_p2id_recipient(target: AccountId, serial_num: Word) -> Result {
let assembler = TransactionKernel::assembler();
let note_code = include_str!("scripts/SWAPP.masm");
...
}
```

The same directory already contains `scripts/P2ID.masm`, which matches the one-input P2ID recipient built by this helper.

### Expected behavior

`build_p2id_recipient()` should load `scripts/P2ID.masm` so the payback note recipient digest commits to the P2ID script that can consume the payback note.