ADR-110: ESP32-C6 firmware extension (#764)

Closes the firmware-side ADR-110 design at v0.7.0-esp32 after a 38-iter /loop SOTA sprint.

Headline (bench, COM9+COM12 ESP32-C6):
- 99.56% cross-board RX, 104.1 µs smoothed offset stdev (≤100 µs §2.4 target met)
- 3.95× EMA suppression, 1.4 ppm crystal skew preserved

4 firmware releases: v0.6.7 / v0.6.8 / v0.6.9 / v0.7.0-esp32.
42 ADR-110 unit tests, 1761 v2 workspace tests, full Firmware CI + QEMU green.

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

@@ -230,9 +230,13 @@ static void swarm_task(void *arg)
         ESP_LOGI(TAG, "Bearer token configured for Seed auth");
     }
 
-    /* Get firmware version string. */
+    /* Firmware version + IP captured locally so logs name the build; both
+     * intentionally unused in the JSON payloads — the seed extracts them
+     * from the register/heartbeat IDs. Keep as side-effect probes. */
     const esp_app_desc_t *app = esp_app_get_description();
-    const char *fw_ver = app ? app->version : "unknown";
+    if (app) {
+        ESP_LOGI(TAG, "swarm bridge fw=%s", app->version);
+    }
 
     /* Get local IP. */
     char ip_str[16];
@@ -278,15 +282,12 @@ static void swarm_task(void *arg)
         xSemaphoreGive(s_mutex);
 
         uint32_t uptime_s = (uint32_t)(esp_timer_get_time() / 1000000ULL);
-        uint32_t free_heap = esp_get_free_heap_size();
         uint32_t ts = (uint32_t)(esp_timer_get_time() / 1000ULL);
 
         /* ---- Heartbeat ---- */
         if ((now - last_heartbeat) >= pdMS_TO_TICKS(s_cfg.heartbeat_sec * 1000U)) {
             last_heartbeat = now;
 
-            bool presence = vit_valid && (vit.flags & 0x01);
-
             /* Heartbeat ID: node_id * 1000000 + 100000 + ts_sec */
             uint32_t hb_id = (uint32_t)s_node_id * 1000000U + 100000U + (uptime_s % 100000U);
             char json[SWARM_JSON_BUF];