Adds an opt-in toggle to skip TLS certificate verification when connecting
to the S3 endpoint, for self-hosted S3-compatible backends (e.g. rustfs,
MinIO) that use self-signed certificates. Exposed in both the store/API
protos and the storage settings UI, mirroring the existing use_path_style
toggle. When enabled, the AWS client uses an HTTP transport with
InsecureSkipVerify; default behavior is unchanged.
This governs backend-initiated S3 calls (uploads, deletes, thumbnails, and
image/document streaming). Video/audio playback redirects the browser to a
presigned URL, so that path still requires the browser to trust the cert.
Closes#6039
