feat(openwrt): add TollGate provision button and direct-download fallback

- OpenWrtGateway.vue: add "Install TollGate" button when not installed;
  tracks connected credentials for reuse in the provision call
- install.rs: fall back to wget download from GitHub releases when the
  package is not in any opkg feed (mips_24kc and other arches supported)
- openwrt.rs: provision-tollgate now falls back to saved router_config
  for credentials, matching the behaviour of get-status

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

core/archipelago/src/api/rpc/openwrt.rs

@@ -136,23 +136,27 @@ impl RpcHandler {
         &self,
         params: Option<serde_json::Value>,
     ) -> Result<serde_json::Value> {
-        let p = params.ok_or_else(|| anyhow::anyhow!("Missing params"))?;
+        let saved = net_router::load_router_config(&self.config.data_dir).await?;
+        let p = params.unwrap_or_default();
 
         let host = p
             .get("host")
             .and_then(|v| v.as_str())
-            .ok_or_else(|| anyhow::anyhow!("Missing host"))?
-            .to_string();
+            .map(|s| s.to_string())
+            .or_else(|| if saved.configured { Some(saved.address.clone()) } else { None })
+            .ok_or_else(|| anyhow::anyhow!("No router configured — provide host or call router.configure first"))?;
         let ssh_user = p
             .get("ssh_user")
             .and_then(|v| v.as_str())
-            .unwrap_or("root")
-            .to_string();
+            .map(|s| s.to_string())
+            .or_else(|| saved.username.clone())
+            .unwrap_or_else(|| "root".to_string());
         let ssh_password = p
             .get("ssh_password")
             .and_then(|v| v.as_str())
-            .unwrap_or("")
-            .to_string();
+            .map(|s| s.to_string())
+            .or_else(|| saved.password.clone())
+            .unwrap_or_default();
 
         let default_mint_url = format!("http://{}:{}", self.config.host_ip, LOCAL_MINT_PORT);
         let mint_url = p