Step 2b: firmware upload (/api/ota) with image checks and rollback self-test

- aes67_ota: GET /api/ota (version, project, build_date, idf, running,
  previous, previous_version, pending_verify, can_rollback), POST
  /api/ota streamed into the inactive slot (4 KiB chunks), POST
  /api/ota/confirm and /api/ota/rollback.
- Rejected before any flash write: bad magic, wrong chip, wrong
  project_name, chip revision outside the image's min/max range.
  esp_ota_end verifies the whole image.
- Self-test on a pending image: IP address plus HTTP 200 from our own
  /api/status within 60 s marks it valid; otherwise mark invalid and
  reboot into the previous slot. A crash before that is rolled back by
  the bootloader.
- CONFIG_AES67_OTA_SELFTEST_FORCE_FAIL (test builds only) forces a
  failed self-test.
- aes67_web: web_reboot_later() shared by /api/reboot and OTA.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

components/aes67_web/include/aes67_web.h

@@ -16,5 +16,8 @@ esp_err_t web_register_uri(const httpd_uri_t *uri);
 // Start httpd on port 80 with the core routes (/, /api/status, /api/config, /api/reboot).
 esp_err_t aes67_web_start(void);
 
+// Restart after ms (lets an HTTP response go out first).
+void web_reboot_later(uint32_t ms);
+
 // Send a cJSON object as the response body (application/json).
 esp_err_t web_send_json(httpd_req_t *req, const cJSON *json);