feat: add OTA firmware update from URL

Wraps esp_https_ota for over-the-air updates via HTTPS.
Dual OTA partitions enable safe rollback.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

main/ota/ota_manager.c

@@ -0,0 +1,33 @@
+#include "ota_manager.h"
+
+#include "esp_log.h"
+#include "esp_ota_ops.h"
+#include "esp_http_client.h"
+#include "esp_https_ota.h"
+
+static const char *TAG = "ota";
+
+esp_err_t ota_update_from_url(const char *url)
+{
+    ESP_LOGI(TAG, "Starting OTA from: %s", url);
+
+    esp_http_client_config_t config = {
+        .url = url,
+        .timeout_ms = 120000,
+        .buffer_size = 4096,
+    };
+
+    esp_https_ota_config_t ota_config = {
+        .http_config = &config,
+    };
+
+    esp_err_t ret = esp_https_ota(&ota_config);
+    if (ret == ESP_OK) {
+        ESP_LOGI(TAG, "OTA successful, restarting...");
+        esp_restart();
+    } else {
+        ESP_LOGE(TAG, "OTA failed: %s", esp_err_to_name(ret));
+    }
+
+    return ret;
+}

main/ota/ota_manager.h

@@ -0,0 +1,12 @@
+#pragma once
+
+#include "esp_err.h"
+
+/**
+ * Perform OTA firmware update from a URL.
+ * Downloads the firmware binary and applies it. Reboots on success.
+ *
+ * @param url  HTTPS URL to the firmware .bin file
+ * @return ESP_OK on success (device will reboot), error code otherwise
+ */
+esp_err_t ota_update_from_url(const char *url);