fix(provisioning): drop the 2-minute QR display delay

The 15s FIRST_IMAGE_POLL_INTERVAL_MS bootstrap already keeps the QR on
the panel (204 responses don't trigger a redraw) until the user claims
via /setup/{mac} and the server's bootstrap-bypass serves an image. The
hard-coded delay(120000) was just dead time between WiFi save and the
first poll — observed in the field as ~110s of nothing happening after
login.

Also touches operation.h header comments to match the "hold until the
screen flashes" terminology and document the short-press fast-poll
gesture.

src/operation.h

@@ -316,13 +316,16 @@ void normal_operation_impl(const String& mac, HTTP& http, const String& url, Pre
     }
 
     esp_sleep_enable_timer_wakeup(sleepMs * 1000ULL);
-    // Wake on the BOOT button so the user-facing 5-second-hold reset works
-    // even during deep sleep. Without this, the button only does anything
-    // during the brief poll-and-paint window when the device is awake, and
-    // a full sleep cycle (default minutes) of holding does nothing.
+    // Wake on the BOOT button so the user-facing "hold until the screen
+    // starts to flash" reset works even during deep sleep. Without this,
+    // the button only did anything during the brief awake window during
+    // a poll, and a full sleep cycle of holding did nothing.
     // Pin is GPIO 0 (PIN_BTN_RESET); active-low because BOOT is pulled-up
     // and shorts to ground on press. After EXT0 wakes the chip, setup()
     // runs and check_reset_button() handles the remainder of the hold.
+    // A too-short press wakes the device but check_reset_button returns
+    // false → normal_operation_impl runs → the next poll fetches a fresh
+    // image, which doubles as a "force refresh" gesture.
     esp_sleep_enable_ext0_wakeup((gpio_num_t)PIN_BTN_RESET, 0);
     esp_deep_sleep_start();
 }