Address review: restore queue-full log, fix power-of-2 comment

- Add HELPER_LOG when overflow buffer is full and connection is dropped
- Clarify comment: defaults are power of 2 (not a requirement for users)

esphome/components/api/__init__.py

@@ -301,7 +301,7 @@ CONFIG_SCHEMA = cv.All(
             # Maximum queued send buffers per connection before dropping connection
             # Each buffer uses ~8-12 bytes overhead plus actual message size
             # Platform defaults based on available RAM and typical message rates:
-            # CONF_MAX_SEND_QUEUE should be a power 2 for best performance
+            # CONF_MAX_SEND_QUEUE defaults are power of 2 for efficient modulo
             cv.SplitDefault(
                 CONF_MAX_SEND_QUEUE,
                 esp8266=4,  # Limited RAM, need to fail fast

esphome/components/api/api_frame_helper.cpp

@@ -150,6 +150,7 @@ APIError APIFrameHelper::write_raw_(const struct iovec *iov, int iovcnt, uint16_
 
   // Queue unsent data into overflow buffer
   if (!this->overflow_buf_.enqueue_iov(iov, iovcnt, total_write_len, skip)) {
+    HELPER_LOG("Overflow buffer full, dropping connection");
     this->state_ = State::FAILED;
     return APIError::SOCKET_WRITE_FAILED;
   }