scripts: switch verify-install.sh from curl to wget

Replace curl with wget for downloading release manifests and
signatures in verify-install.sh. wget handles redirects, retries, and
error reporting more robustly by default, which avoids silent download
failures that caused misleading "Invalid signature!" errors.

Also add error checking to all download calls so failures are reported
immediately with the URL that failed, and log which signature file and
user failed gpg verification.

Dockerfile

@@ -29,13 +29,13 @@ FROM alpine as final
 VOLUME /root/.lnd
 
 # Add utilities for quality of life and SSL-related reasons. We also require
-# curl and gpg for the signature verification script.
+# wget and gpg for the signature verification script.
 RUN apk --no-cache add \
     bash \
     jq \
     ca-certificates \
     gnupg \
-    curl
+    wget
 
 # Copy the binaries from the builder image.
 COPY --from=builder /go/bin/lncli /bin/