feat(lightning): channel open fee control, channels tab in wallet settings, mempool tx link

- Fee selector on channel open: Standard (~6 blocks) / Medium (~3) /
  Fast (next block) presets, or custom target confirmations / sat/vB;
  backend validates and passes target_conf / sat_per_vbyte to LND
- Extract channel management into LightningChannelsPanel, reused by the
  LND channels page and a new Channels tab in the Wallet Settings modal
- Funding tx link on each channel card opens the node's mempool app at
  /tx/<txid>

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

core/archipelago/src/api/rpc/lnd/channels.rs

@@ -203,6 +203,29 @@ impl RpcHandler {
             .and_then(|v| v.as_bool())
             .unwrap_or(false);
 
+        // Fee control: either a confirmation target or an explicit fee rate
+        let target_conf = params.get("target_conf").and_then(|v| v.as_i64());
+        let sat_per_vbyte = params.get("sat_per_vbyte").and_then(|v| v.as_i64());
+        if target_conf.is_some() && sat_per_vbyte.is_some() {
+            return Err(anyhow::anyhow!(
+                "Invalid fee parameters: specify either target_conf or sat_per_vbyte, not both"
+            ));
+        }
+        if let Some(tc) = target_conf {
+            if !(1..=1008).contains(&tc) {
+                return Err(anyhow::anyhow!(
+                    "Invalid target_conf: must be between 1 and 1008 blocks"
+                ));
+            }
+        }
+        if let Some(rate) = sat_per_vbyte {
+            if !(1..=5000).contains(&rate) {
+                return Err(anyhow::anyhow!(
+                    "Invalid sat_per_vbyte: must be between 1 and 5000"
+                ));
+            }
+        }
+
         info!(
             peer = pubkey,
             amount = amount,
@@ -250,11 +273,18 @@ impl RpcHandler {
             }
         }
 
-        let open_body = serde_json::json!({
+        let mut open_body = serde_json::json!({
             "node_pubkey_string": pubkey,
             "local_funding_amount": amount.to_string(),
             "private": private,
         });
+        if let Some(tc) = target_conf {
+            open_body["target_conf"] = serde_json::json!(tc);
+        }
+        if let Some(rate) = sat_per_vbyte {
+            // LND REST encodes uint64 as a JSON string
+            open_body["sat_per_vbyte"] = serde_json::json!(rate.to_string());
+        }
 
         let resp = client
             .post(format!("{LND_REST_BASE_URL}/v1/channels"))