Default a scheme-less s3.* endpoint to TLS (closes #158)

With the s3.* config form and an endpoint written without a scheme, use_ssl being omitted built an http:// endpoint, while config.example.yml documented use_ssl as defaulting to true. Over plain HTTP a network observer sees manifests, object names, sizes and the access key id, and can alter responses.

use_ssl is now *bool: omitted (nil) means the default, TLS; only an explicit use_ssl: false forces plain HTTP. This matches the s3:// URL form, which already defaults to TLS. The config init template dropped its misleading use_ssl line from the s3:// block (that key is never read for URLs; ?ssl=false controls TLS there) and points at ?ssl=false instead.

Model: opus-4-8

internal/storage/module.go

@@ -111,10 +111,11 @@ func storerFromParsedS3URL(parsed *URL, cfg *config.Config) (Storer, error) {
 func storerFromLegacyS3Config(cfg *config.Config) (Storer, error) {
 	endpoint := cfg.S3.Endpoint
 
-	// Ensure protocol is present
+	// Ensure protocol is present. Absent an explicit use_ssl, default to TLS;
+	// plain HTTP only when use_ssl is written as false.
 	if !strings.HasPrefix(endpoint, "http://") &&
 		!strings.HasPrefix(endpoint, "https://") {
-		if cfg.S3.UseSSL {
+		if cfg.S3.UseSSL == nil || *cfg.S3.UseSSL {
 			endpoint = "https://" + endpoint
 		} else {
 			endpoint = "http://" + endpoint