fix(provisioning): stop redrawing the QR on every poll, add WiFi-fail retry screen

Two related fixes that together let the post-WiFi-setup window be quiet:

1. operation.h 204/404: skip the panel redraw entirely. The panel already
   holds the right thing — setup QR if no image has ever been painted
   (img_id == -1), or a real photo if img_id >= 0. Redrawing the QR every
   15s during the bootstrap claim window put the e-ink into a perpetual
   ~20s mid-refresh loop and risked ghosting. Tests updated to assert
   no redraw on either sub-case.

2. main.cpp WiFi-fail path: drop the epd_fill(RED) + 3s delay + AP
   re-redraw sequence (~43s of e-ink work that destroyed the QR mid-flow)
   and replace with a single repaint of a new "Connection Failed — try
   again" Step 1/2 screen with red accents. gen_screens.py grows a
   gen_ap_retry() variant that recolors yellow → red and swaps the
   header/QR labels; the result is shipped as ap_bg_retry.bin alongside
   ap_bg.bin in LittleFS. epd.h exposes epd_draw_ap_screen_retry().

src/panels/waveshare73/v1/epd_driver.cpp

@@ -179,6 +179,12 @@ void epd_draw_ap_screen(QRCode* qr) {
     draw_from_lfs("/ap_bg.bin", COLOR_YELLOW, qr, 563, 185, 5);
 }
 
+void epd_draw_ap_screen_retry(QRCode* qr) {
+    // Same QR coordinates — only the bg .bin differs (red accents,
+    // "Connection Failed — try again" label).
+    draw_from_lfs("/ap_bg_retry.bin", COLOR_RED, qr, 563, 185, 5);
+}
+
 void epd_draw_setup_screen(QRCode* qr) {
     // SETUP_QR_X=553, SETUP_QR_Y=175, SETUP_QR_CELL=5  (must match gen_screens.py)
     draw_from_lfs("/setup_bg.bin", COLOR_GREEN, qr, 553, 175, 5);