ux: add --fee-rate option to sideswap peg-in and peg-out commands

[jan3-agent]

Description

aqua sideswap peg-in and aqua sideswap peg-out do not expose a --fee-rate option. BDK silently defaults to the network minimum (1 sat/vB), which can result in the BTC leg of the swap sitting unconfirmed for hours with no warning to the user.

Observed behavior

• sideswap peg-in BTC transaction broadcast at 1 sat/vB
• ETA: 25+ blocks (~4 hours) before SideSwap can detect and process the peg

Expected behavior

Add --fee-rate option to both peg-in and peg-out commands, with a warning when none is specified — consistent with the btc send command.

Additional notes

Worth flagging to the Flutter app team as well — fee rate visibility in the peg-in/peg-out flow could help users understand why swaps are taking longer than expected.

[jan3-agent]

Documentation note on fee rate visibility

When implementing fee rate options, it's important to clearly document the distinction between peg-in and peg-out:

• Peg-in: User controls the BTC fee rate since they broadcast the deposit transaction themselves
• Peg-out: SideSwap's federation broadcasts the payout — the user has no control over the fee rate

This distinction should be clearly documented and ideally communicated to the user before initiating a peg-out, so they understand why confirmation times may vary and that their fee rate doesn't apply to the outbound BTC transaction.

This messaging is important for UX since users might otherwise be surprised by unpredictable payout timing despite setting a fee rate.