Never physically refresh the panel with a short/wrong-size frame

Found on hardware: the Tools Server field was pointed at Immich's own
port instead of the frame server's, so /frame/image was actually hitting
Immich and getting back a small error response (~10KB) instead of a
192,000-byte frame. epd_display_stream() logged a size-mismatch warning
but called epd_turn_on_display() anyway, physically refreshing the panel
with a buffer that was ~95% whatever was left over from before -- visible
as "garbage" on screen, overwriting a previously-good image.

epd_display_stream() now returns ESP_ERR_INVALID_SIZE instead of
refreshing when the stream doesn't supply exactly EPD_FRAME_BYTES. Since
this check happens before epd_turn_on_display() is ever called, the
pixel data that *did* arrive only ever reached the panel's internal RAM
over SPI, not the physically visible display, so aborting here leaves the
screen exactly as it was.

This also means fetch_and_display() failing now always implies the panel
was never touched -- simplified frame_client_run() accordingly (dropped
the now-always-true/false out-param that used to distinguish "failed
before vs. during streaming", and always shows the FAILED status screen
on any fetch/display error, since it's now guaranteed safe to do so).

firmware/components/epd7in3e/epd7in3e.c

@@ -234,7 +234,17 @@ esp_err_t epd_display_stream(epd_read_fn_t read_fn, void *ctx)
     EPD_CHECK(err);
 
     if (total != EPD_FRAME_BYTES) {
-        ESP_LOGW(TAG, "Stream supplied %u bytes, expected %u", (unsigned)total, (unsigned)EPD_FRAME_BYTES);
+        /* Whatever was received has already been clocked into the panel's
+         * internal RAM over SPI, but epd_turn_on_display() (the actual
+         * physical refresh trigger) hasn't been called yet -- returning
+         * here instead leaves the visible screen exactly as it was, rather
+         * than refreshing onto a mostly-garbage buffer. Confirmed on
+         * hardware: a misdirected fetch that returned a ~10KB error page
+         * instead of a 192,000-byte frame still triggered a refresh before
+         * this check existed, painting garbage over a previously-good image. */
+        ESP_LOGE(TAG, "Stream supplied %u bytes, expected %u -- aborting refresh",
+                 (unsigned)total, (unsigned)EPD_FRAME_BYTES);
+        return ESP_ERR_INVALID_SIZE;
     }
 
     return epd_turn_on_display();