refactor: fix SC2154 warnings for SSH_OPTS in provider libraries

Added shellcheck directive comments before first SSH_OPTS usage in:
- aws-lightsail/lib/common.sh
- gcp/lib/common.sh
- lambda/lib/common.sh
- vultr/lib/common.sh
- linode/lib/common.sh
- hetzner/lib/common.sh
- digitalocean/lib/common.sh

SSH_OPTS is defined in shared/common.sh but shellcheck can't detect
cross-file variable definitions, so we suppress the warning with
an explanatory comment.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

digitalocean/lib/common.sh

@@ -241,6 +241,8 @@ for net in data['droplet']['networks']['v4']:
 verify_server_connectivity() {
     local ip="$1"
     local max_attempts=${2:-30}
+    # SSH_OPTS is defined in shared/common.sh
+    # shellcheck disable=SC2154
     generic_ssh_wait "$ip" "$SSH_OPTS -o ConnectTimeout=5" "echo ok" "SSH connectivity" "$max_attempts" 5
 }