Fix web radio reconnect busy-loop on non-2xx HTTP status

openStream() only established the TCP/TLS connection; it never checked
the HTTP status code. A 4xx/5xx response (wrong stream path, station
temporarily down, etc.) still returned a valid client handle, so
streamWhileEnabled() entered its pump loop, immediately read 0 bytes
(no body), and returned -- skipping the kReconnectDelay branch
entirely, which only fired when openStream() itself returned nullptr.
run()'s outer loop then retried immediately: a full TCP+TLS handshake
in a tight loop bounded only by network RTT, not the intended 5s
backoff -- observed live at roughly 2 attempts/second.

This mattered beyond wasted reconnects: a concurrent full FM band scan
(POST /api/tuner/scan/full, which legitimately takes 70-135s) lost its
HTTP connection outright while this loop was running, before this fix.
After adding the status-code check and routing non-2xx through the
same reconnect delay as a failed connection, the same scan completed
cleanly twice in a row under the same conditions.

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

Software/main/web_radio_stream.cpp

@@ -190,6 +190,25 @@ void streamWhileEnabled(webradio::WebRadioService& service,
         return;
     }
 
+    // esp_http_client_open() only establishes the TCP/TLS connection; a 4xx/
+    // 5xx HTTP response (wrong path, station offline, etc.) still returns a
+    // valid client handle here. Without this check, such a response reads
+    // as an empty body -> pumpOneFrame() returns false on its first call ->
+    // the reconnect delay below is skipped entirely, and run()'s outer loop
+    // immediately retries: a full TCP+TLS handshake in a tight loop, bounded
+    // only by network RTT, not kReconnectDelay. Observed live 2026-08-26 at
+    // roughly 2 attempts/second against a misconfigured URL, competing for
+    // CPU/heap with an unrelated concurrent FM scan on the same board.
+    const int status = esp_http_client_get_status_code(client);
+    if (status < 200 || status >= 300) {
+        ESP_LOGW(kTag, "stream %s returned HTTP %d, not audio -- backing off",
+                 url.c_str(), status);
+        esp_http_client_close(client);
+        esp_http_client_cleanup(client);
+        vTaskDelay(kReconnectDelay);
+        return;
+    }
+
     InputBuffer in;
     bool loggedFormat = false;
     while (service.config().enabled