feat: add boltz savings swap

[coreyphillips]

This PR adds a swap-based path for transferring spending balance to savings, so Lightning funds can move on-chain through a Boltz reverse swap instead of only by closing a channel. It ports the equivalent Android feature (synonymdev/bitkit-android#1081) to iOS.

Description

• Adds a Boltz reverse swap flow to the transfer-to-savings journey. The confirm screen now shows a live quote (amount to savings, network fee, service fee, and the amount you will receive) and lets the user proceed with a swap or fall back to closing the channel.
• Guards against amounts that are too low to swap, holding back a small reserve for Lightning routing fees and surfacing a clear message when the amount cannot be transferred.
• Waits for the on-chain claim during the progress step and resumes any pending swaps when the wallet starts, refreshing balances automatically once a swap lands on-chain. The updates stream stops with the node and restarts on the next wallet start.
• Adds a Swaps section under Dev Settings to list swaps and claim a reverse swap, backed by a new service that wraps the Boltz module. The manual claim button only shows while the swap is actually claimable (lockup on-chain and no claim broadcast yet).
• Adds a reusable continuous amount slider component used by the swap amount controls.
• Bumps bitkit-core to 0.5.1, which introduces the Boltz module this flow depends on. The bump is purely additive over 0.4.1 (verified against the published Swift bindings).

Linked Issues/Tasks

Android counterpart: synonymdev/bitkit-android#1081

QA Notes

Manual Tests

• 1. With a spending balance, Transfer to Savings → Savings Confirm: quote shows amount to savings, network fee, service fee, and you'll receive.
• 2. Savings Confirm → drag the amount slider: quote recomputes for the new amount.
• 3. Savings Confirm with a balance below the swap minimum: amount-too-low message shows and swipe does nothing.
• 4a. Savings Confirm → swipe to confirm → Savings Progress: completes after the on-chain claim.
  • 4b. After claim: savings balance reflects the swapped funds without a manual sync.
• 5. regression: Savings Confirm → Close channel instead: falls back to the channel-close path.
• 6. regression: Start the app with a pending swap: swap resumes and balance updates once it lands on-chain.
• 7a. Dev Settings → Swaps → tap a swap → Swap Details: Claim now shows only for an unclaimed reverse swap with its lockup in mempool or confirmed.
  • 7b. Swap Details of a created, expired, refunded, or claimed swap: no Claim button.

Automated Checks

• Unit tests added: savings swap quote fee breakdown and claimable status gating in SavingsSwapTests.swift.
• Ran locally against bitkit-core 0.5.1: simulator Debug build and translation validation pass.