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/wasm_runtime.c

@@ -12,6 +12,9 @@
 
 #include "sdkconfig.h"
 #include "wasm_runtime.h"
+#include "nvs_config.h"
+
+extern nvs_config_t g_nvs_config;
 
 #if defined(CONFIG_WASM_ENABLE) && defined(WASM3_AVAILABLE)
 
@@ -380,11 +383,7 @@ static void send_wasm_output(uint8_t slot_id)
     memset(&pkt, 0, sizeof(pkt));
 
     pkt.magic = WASM_OUTPUT_MAGIC;
-#ifdef CONFIG_CSI_NODE_ID
-    pkt.node_id = (uint8_t)CONFIG_CSI_NODE_ID;
-#else
-    pkt.node_id = 0;
-#endif
+    pkt.node_id = g_nvs_config.node_id;
     pkt.module_id = slot_id;
     pkt.event_count = n_filtered;