fix: expose min_funding_satoshis via Config

Add `min_funding_sats` field to `Config` that maps to LDK's
`ChannelHandshakeLimits::min_funding_satoshis`. This allows server
operators to enforce a higher minimum channel funding amount for
inbound channels, overriding the default of 1000 sats.

Fixes #842

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: vincenzopalazzo

src/config.rs

@@ -125,6 +125,7 @@ pub(crate) const LNURL_AUTH_TIMEOUT_SECS: u64 = 15;
 /// | `node_alias`                           | None               |
 /// | `trusted_peers_0conf`                  | []                 |
 /// | `probing_liquidity_limit_multiplier`   | 3                  |
+/// | `min_funding_sats`                     | None               |
 /// | `anchor_channels_config`               | Some(..)           |
 /// | `route_parameters`                     | None               |
 /// | `tor_config`                           | None               |
@@ -167,6 +168,17 @@ pub struct Config {
 	/// Channels with available liquidity less than the required amount times this value won't be
 	/// used to send pre-flight probes.
 	pub probing_liquidity_limit_multiplier: u64,
+	/// The minimum funding amount in satoshis that we require from channel counterparties when
+	/// they open inbound channels to us.
+	///
+	/// Channels with funding below this value will be rejected.
+	///
+	/// If unset, the `rust-lightning` default of `1000` sats will be used.
+	///
+	/// Please refer to [`ChannelHandshakeLimits::min_funding_satoshis`] for further details.
+	///
+	/// [`ChannelHandshakeLimits::min_funding_satoshis`]: lightning::util::config::ChannelHandshakeLimits::min_funding_satoshis
+	pub min_funding_sats: Option<u64>,
 	/// Configuration options pertaining to Anchor channels, i.e., channels for which the
 	/// `option_anchors_zero_fee_htlc_tx` channel type is negotiated.
 	///
@@ -210,6 +222,7 @@ impl Default for Config {
 			announcement_addresses: None,
 			trusted_peers_0conf: Vec::new(),
 			probing_liquidity_limit_multiplier: DEFAULT_PROBING_LIQUIDITY_LIMIT_MULTIPLIER,
+			min_funding_sats: None,
 			anchor_channels_config: Some(AnchorChannelsConfig::default()),
 			tor_config: None,
 			route_parameters: None,
@@ -339,6 +352,9 @@ pub(crate) fn default_user_config(config: &Config) -> UserConfig {
 	// will mostly be relevant for inbound channels.
 	let mut user_config = UserConfig::default();
 	user_config.channel_handshake_limits.force_announced_channel_preference = false;
+	if let Some(min_funding_sats) = config.min_funding_sats {
+		user_config.channel_handshake_limits.min_funding_satoshis = min_funding_sats;
+	}
 	user_config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx =
 		config.anchor_channels_config.is_some();
 	user_config.reject_inbound_splices = false;