fix(firmware): use NVS node_id instead of Kconfig constant (#279)

CONFIG_CSI_NODE_ID (compile-time, always 1) was hardcoded in 6
places: CSI frame serialization, compressed frames, vitals packets,
WASM output packets, and display UI. NVS provisioning wrote the
correct node_id but it was never used at runtime.

Fixed all occurrences to use g_nvs_config.node_id:
- csi_collector.c: frame header + log message
- edge_processing.c: compressed frame + vitals packet
- wasm_runtime.c: WASM output packet
- display_ui.c: system info display

This means --node-id 0/1/2 provisioning now actually works for
multi-node mesh deployments.

Closes #279

Co-Authored-By: claude-flow <ruv@ruv.net>

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

@@ -7,8 +7,11 @@
  */
 
 #include "display_ui.h"
+#include "nvs_config.h"
 #include "sdkconfig.h"
 
+extern nvs_config_t g_nvs_config;
+
 #if CONFIG_DISPLAY_ENABLE
 
 #include <stdio.h>
@@ -347,11 +350,7 @@ void display_ui_update(void)
     {
         char buf[48];
 
-#ifdef CONFIG_CSI_NODE_ID
-        snprintf(buf, sizeof(buf), "Node: %d", CONFIG_CSI_NODE_ID);
-#else
-        snprintf(buf, sizeof(buf), "Node: --");
-#endif
+        snprintf(buf, sizeof(buf), "Node: %d", g_nvs_config.node_id);
         lv_label_set_text(s_sys_node, buf);
 
         snprintf(buf, sizeof(buf), "Heap: %lu KB free",