fix: configure routing params for single lsp

[ovitrif]

This PR configures explicit LDK routing parameters optimized for the single-LSP topology that most users operate in.

Description

The default RouteParametersConfig from LDK may be too restrictive for our setup where most users route all payments through a single LSP. This adds explicit routing parameters to the node config:

1. Removes routing fee cap (maxTotalRoutingFeeMsat = null) to avoid rejecting valid routes
2. Sets CLTV expiry delta to 1008 blocks (~1 week)
3. Allows up to 10 multi-path payment splits for better payment success
4. Lowers channel saturation threshold for more aggressive channel utilization

Preview

N/A - no UI changes

QA Notes

1. Outbound Lightning payment

1. Build and install a dev build
2. Send a Lightning payment of a small amount through the default LSP
3. Verify the payment completes successfully

2. Varying amounts

1. Send payments of varying sizes (small, medium, larger)
2. Verify all payments route and complete successfully

3. Receive payment

1. Generate a Lightning invoice
2. Pay it from an external wallet
3. Verify the payment is received successfully

4. Regression check

1. Verify channel opens with the LSP still succeed
2. Verify on-chain transactions still work as expected