improve linux-ssh-operator-skill: bug fixes, rsync support, tunneling docs

- Fix dry-run bug in ssh_alias_setup.sh (pub key check skipped when key was never generated)
- Remove dead code in ssh_run.sh (-- check after host arg was never reachable)
- Add --rsync/--delete flags to ssh_copy.sh for incremental rsync transfers
- Add -C/--compress flag to ssh_run.sh for slow-link connections
- Expand SKILL.md/SKILL.zh-CN.md: tunneling, jump host, SSH multiplexing, Docker ops
- Expand ssh-playbook.md: port forwarding, bastion, ControlMaster, structured troubleshooting table

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

linux-ssh-operator-skill/scripts/ssh_alias_setup.sh

@@ -118,7 +118,7 @@ if [[ ! -f "$key" ]]; then
   fi
 fi
 
-if [[ ! -f "$key_pub" ]]; then
+if ! $dry_run && [[ ! -f "$key_pub" ]]; then
   echo "Public key not found: $key_pub" >&2
   exit 1
 fi