fix(firmware): capture DATA frames on display-less boards — #893/#866/#897

The pre-built binaries set a MGMT-only promiscuous filter
(WIFI_PROMIS_FILTER_MASK_MGMT) as the #396 workaround — DATA-frame
interrupt load races the QSPI display's SPI traffic against the SPI-flash
cache and crashes Core 0 in wDev_ProcessFiq. But MGMT-only fires the CSI
callback only on sparse management frames, so on the common DISPLAY-LESS
boards (DevKitC-1, T7-S3, N8R8) CSI yield collapses to 0 pps under real
traffic (#521) — the node looks dead despite being on the network, which
is the root cause of most "can't reproduce / it's fake" reports (#804/#37).

A board with no AMOLED panel has no QSPI/SPI-flash contention, so it can
safely capture DATA frames. After the boot-time display probe runs:
  - display present  -> keep MGMT-only (preserve #396 crash protection)
  - no display       -> upgrade filter to MGMT|DATA (restore CSI yield)

Implementation (runtime-gated, no boot reorder):
  - display_task.c: s_display_active flag + display_is_active() accessor,
    set true only when the panel is detected and the display task starts.
  - csi_collector.c: csi_collector_enable_data_capture() re-sets the
    promiscuous filter to MGMT|DATA.
  - main.c: after display_task_start(), if !display_is_active() (or display
    support not compiled in), upgrade the filter.

Build-verified on BOTH targets: esp32c6 (headless path) and esp32s3
(display path, display_task.c compiled) — Project build complete, RC 0.
Needs on-hardware confirmation that yield recovers and no #396 crash.

firmware/esp32-csi-node/main/display_task.c

@@ -9,6 +9,14 @@
 #include "display_task.h"
 #include "sdkconfig.h"
 
+/* Set true once an AMOLED panel is detected and the display task starts.
+ * Defined outside the CONFIG_DISPLAY_ENABLE guard so display_is_active()
+ * exists on headless builds too (where it stays false → CSI captures DATA
+ * frames; see RuView#893). */
+static bool s_display_active = false;
+
+bool display_is_active(void) { return s_display_active; }
+
 #if CONFIG_DISPLAY_ENABLE
 
 #include <string.h>
@@ -162,6 +170,7 @@ esp_err_t display_task_start(void)
 
     ESP_LOGI(TAG, "Display task started (Core %d, priority %d, %d fps)",
              DISP_TASK_CORE, DISP_TASK_PRIORITY, DISP_FPS_LIMIT);
+    s_display_active = true;
     return ESP_OK;
 }