Add POST_TO_API_DONE idempotency guard to post_to_api() to prevent
the same telemetry record from being submitted twice with the same
RANDOM_UUID. This mirrors the existing POST_UPDATE_DONE pattern in
post_update_to_api().
post_to_api() is called twice in build.func:
- After storage validation (inside CONTAINER_STORAGE check)
- After create_lxc_container() completes
When both execute, the second call fails with a random_id uniqueness
violation on PocketBase, generating server-side errors.
5ee4f4e34b