fix: use fast fee for hw transfer

[piotr-iohk]

Fixes #633

This PR makes Trezor → spending funding use the same fast on-chain fee rate as savings → spending, so LSP channel funding confirms more reliably.

Description

• Uses the fast fee tier for hardware-wallet transfer funding instead of the settings default (normal), which can resolve to 1 sat/vB in a quiet fee market.
• Raises the estimate-unavailable fallback from 1 to 3 sat/vB so compose still picks a usable rate when fee estimates are missing.
• Updates fee-reserve unit coverage for the new fallback floor.

Related Android: synonymdev/bitkit-android#1088

Linked Issues/Tasks

• [Bug]: Trezor transfer to spending uses low on-chain fee rate #633
• Epic: epic: Trezor Hardware Wallet UI #589

Screenshot / Video

N/A

QA Notes

Manual Tests

• 1. Pair Trezor with spendable UTXOs → Transfer → Spending → Sign: funding tx uses a fast-tier sat/vB (check explorer), not ~1 sat/vB when the market’s mid is 1.
• 2. Complete HW transfer → Spending: funding confirms and the transfer progresses toward channel open without lingering unconfirmed for hours under a normal fee market.
• 3. regression: Savings → Transfer → Spending: still uses fast and completes as before.

Automated Checks

• Unit tests modified: update fee-reserve floor expectation (3 × 1200) in HwFundingSignerTests.swift.
• Local: xcodebuild test for HwFundingSignerTests.
• CI: standard build and test checks run by the PR bot.

Made with Cursor

[greptile-apps]

Greptile Summary

This PR increases the fee rate used for hardware-wallet funding. The main changes are:

• Uses the fast fee tier for hardware-wallet transfers to spending.
• Raises the unavailable-estimate fallback from 1 to 3 sat/vB.
• Updates the reserve-floor test and changelog.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.
• The fast-tier conversion is a safe numeric widening.
• The composition and reserve paths consistently use the new fallback.
• Balance subtraction remains guarded when the reserve exceeds the balance.

Important Files Changed

Filename	Overview
Bitkit/AppScene.swift	Selects the fast fee tier for hardware-wallet funding.
Bitkit/ViewModels/HwFundingSigner.swift	Raises the fallback fee-rate defaults from 1 to 3 sat/vB.
BitkitTests/HwFundingSignerTests.swift	Updates the fallback reserve-floor expectation to 3,600 sats.
changelog.d/next/633.fixed.md	Documents the faster hardware-wallet funding fee.

_{Reviews (1): Last reviewed commit: "chore: rename changelog fragment" | Re-trigger Greptile}

[piotr-iohk]

Tested end-to-end on mainnet (Trezor → spending / Blocktank channel open).

• Funding tx used ~2 sat/vB (Blocktank fast; not the previous ~1 sat/vB mid/default path).
• Tx confirmed within minutes and the channel opened successfully.
• Previously the same flow could sit unconfirmed for hours at ~1 sat/vB.

Fix confirmed end-to-end on mainnet.

[pwltr]

utACK