fix(api): disable reqwest connection pool

Direct mycelium runs and our pkexec spawns are both healthy
(sidecar logs show acquired routes streaming for 20+s). Yet our
reqwest poller can't reach 127.0.0.1:port after the first
successful request. Smoking gun: failure happens ~10s after the
first reply — exactly when an idle keep-alive connection would
have been reaped.

Disable pooling (pool_max_idle_per_host(0)) so every call opens a
fresh TCP connection. Loopback overhead is negligible (~50us per
request) and we're immune to server-side idle closes. Also pin
connect_timeout to 3s so a wedged half-open doesn't block for
the full 10s request timeout.

src-tauri/src/api/mod.rs

@@ -22,8 +22,15 @@ pub struct MyceliumClient {
 
 impl MyceliumClient {
     pub fn new(base: impl Into<String>) -> Self {
+        // Mycelium's HTTP server seems to drop idle keep-alive connections
+        // around the 10s mark; reusing a pooled stale connection surfaces
+        // as a generic "error sending request" once `start_daemon`
+        // returned. Open a fresh TCP connection per request — overhead is
+        // negligible on loopback and immune to server-side closes.
         let http = Client::builder()
+            .pool_max_idle_per_host(0)
             .timeout(Duration::from_secs(10))
+            .connect_timeout(Duration::from_secs(3))
             .build()
             .expect("reqwest client build");
         Self {