Swap saga (#1183)

# Implement Saga Pattern for Swap Operations with Recovery Mechanism

## Overview

This PR refactors the swap operation implementation to use the saga pattern - a distributed transaction pattern that provides reliable transaction management through explicit state tracking and compensation-based error handling. The implementation includes a robust recovery mechanism that automatically handles swap operations interrupted by crashes, power loss, or network failures.

## What Changed

**Saga Pattern Implementation:**
- Introduced a strict linear state machine for swaps: `Initial` → `SetupComplete` → `Signed` → `Completed`
- New modular `swap_saga` module with state validation, compensation logic, and saga orchestration
- Automatic rollback of database changes on failure, ensuring atomic swap operations
- Replaced previous swap implementation (`swap.rs`, `blinded_message_writer.rs`) with saga-based approach

**Recovery Mechanism:**
- Added `operation_id` and `operation_kind` columns to database schema for tracking which operation proofs belong to
- New `recover_from_bad_swaps()` method that runs on mint startup to handle incomplete swaps
- For proofs left in `PENDING` state from swap operations:
  - If blind signatures exist: marks proofs as `SPENT` (swap completed but not finalized)
  - If no blind signatures exist: removes proofs from database (swap failed partway through)
- Database migrations included for both PostgreSQL and SQLite

crates/cdk-mintd/src/lib.rs

@@ -1183,11 +1183,6 @@ pub async fn run_mintd_with_shutdown(
 
     let mint = Arc::new(mint);
 
-    // Checks the status of all pending melt quotes
-    // Pending melt quotes where the payment has gone through inputs are burnt
-    // Pending melt quotes where the payment has **failed** inputs are reset to unspent
-    mint.check_pending_melt_quotes().await?;
-
     start_services_with_shutdown(
         mint.clone(),
         settings,