fix: harden config loading and ssh addresses, stop resolver on API errors

- read netssh.yaml from the user config directory only, not from the
  working directory
- refuse addresses from NetBox or the cache that are neither an IP
  address nor a hostname (ssh read "-oProxyCommand=…" as an option)
- resolver chain stops at an API failure; only "no address" falls
  through to the next strategy
- netssh --help and -h show netssh's help
- start at most one background cache refresh per 5 minutes
- validate the legacy netbox.url
- page through all IP addresses of a host
- CI: run format check, vet, and tests on pull requests and main
- changelog for v0.0.25

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

cmd/netssh/uninstall.go

@@ -71,6 +71,7 @@ func buildUninstallPlan(cfg *config.Config, keepConfig bool) uninstallPlan {
 			addPath(path)
 			addPath(path + ".lock")
 			addPath(filepath.Join(filepath.Dir(path), "last_refresh"))
+			addPath(filepath.Join(filepath.Dir(path), "refresh_attempt"))
 			if strings.HasPrefix(filepath.Base(filepath.Dir(path)), "instances-") {
 				addPath(filepath.Dir(path))
 			}