Simplify firmware: manage overlay now composited server-side

Deletes manage_qr_overlay.c/.h; frame_client.c's manage-button flow is
now one fetch with &manage=1 instead of on-device QR/text generation
plus separate photo-info/face-labels requests.

firmware/main/frame_client.h

@@ -33,12 +33,13 @@ esp_err_t frame_wifi_connect_sta(const frame_config_t *cfg);
  * deep-sleep until the next refresh.
  *
  * If show_management_qr is true (the manage button was held), the
- * displayed photo gets a small "scan to manage" QR overlay in the
- * top-right corner linking to the server's config page, held for 30
- * seconds (the device stays awake), then reverted back to the plain
- * photo before proceeding to the normal sleep-interval logic. Its
- * battery indicator shows the server's last-known reading, not a fresh
- * one -- see fetch_photo_info() in frame_client.c.
+ * request for that cycle carries &manage=1, and the server bakes its
+ * whole manage overlay (scan-to-manage QR, battery, location/date,
+ * share-QR, named face labels) directly into the image it returns --
+ * see server/app/manage_overlay.py; this device is otherwise unaware
+ * any of that exists, it just displays whatever comes back. Held for 30
+ * seconds (the device stays awake), then reverted back to a plain fetch
+ * before proceeding to the normal sleep-interval logic.
  *
  * Reads the battery (see battery_read_percent()) itself, once, after the
  * photo is already on the panel, and reports it to the server on a