fix: factor HL funding into comparison (use netCostUsd not feesUsd)

[Flotapponnier]

Previously funding was only displayed, not factored into the savings calculation.

Now:

• walletStats for HL returns netCostUsd (fees − funding) instead of feesUsd
• aToBSim/bToASim feesActual = aFees - fundingUsd so saved = gainsEquiv - netCost
• walletFees() in client returns netCostUsd → big number shows true net cost
• Effective bps note: "X.XX bps net (fees + funding)"
• "bps avg · net of funding" subtitle when funding is non-zero

Gains borrowing fees not included (requires separate GnsRolloverFeeCharged scan).