fix: use send-all fee for channel funding

[ovitrif]

This PR fixes the fee estimation for channel funding when using the full onchain balance.

Description

getMaxChannelFundableAmount() was using calculateTotalFee() which builds a regular transaction and fails with "Coin selection failed" when funding a channel with the entire balance (produces dust change). This switches to estimateSendAllFee() which is designed for drain transactions, matching the pattern already used in getMaxSendAmount().

Preview

No UI changes, fixes bug causing error in logs about estimating fee for full wallet balance.

QA Notes

1. Verify app logs don't show these errors anymore:

2026-03-05 13:16:46.100 ERROR   [ldk_node::wallet:1173]              Failed to create transaction: Coin selection failed
2026-03-05 13:16:46.101 WARN    [LightningService.kt:867]            Error calculating fee for 1000 sats to bcrt1pr0kc8wpe8x2pekxfzcfc5ax4p3ak5gwy25ushfp2f67fglkde67qflgpsa, null UTXOs, satsPerVByte=1 [OnchainTxCreationFailed='On-chain transaction could not be created.'] - LightningService
2026-03-05 13:16:46.104 WARN    [LightningRepo.kt:1107]              calculateTotalFee error, using fallback of '1000' [AppError='LDK Node error: Failed to create on-chain transaction.'] - LightningRepo

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