feat: add netssh uninstall

Remove everything netssh and install.sh set up, also leftovers of
older versions:

- netssh blocks and unmarked legacy lines in bash, zsh, and fish
  profiles
- completion files for bash, zsh (incl. the oh-my-zsh cache), fish,
  and the command alias; files not generated by netssh are kept
- the cache directory with hosts, aliases, and per-instance caches
- the config file and local notes; the config is first copied to a
  private netssh.yaml.backup-<timestamp> because it holds API tokens
- the netssh binary; for protected paths the sudo command is printed

--keep-config keeps config and notes, --dry-run only lists the plan,
and --yes skips the confirmation.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/hook/completion.go

@@ -114,3 +114,46 @@ complete --command %s --wraps netssh
 `, completionMarker, alias)
 	}
 }
+
+// CompletionFiles lists the completion and alias files netssh may have
+// installed for itself and for the given command aliases.
+func CompletionFiles(aliases ...string) []string {
+	files := []string{
+		filepath.Join(os.Getenv("HOME"), ".local", "share", "bash-completion", "completions", "netssh"),
+		filepath.Join(ZshFuncDir(), "_netssh"),
+		filepath.Join(FishConfigDir(), "completions", "netssh.fish"),
+		FishAliasesPath(),
+	}
+	// oh-my-zsh caches generated completions separately.
+	for _, dir := range []string{os.Getenv("ZSH_CACHE_DIR"), filepath.Join(os.Getenv("ZSH"), "cache"), filepath.Join(os.Getenv("HOME"), ".oh-my-zsh", "cache")} {
+		if dir != "" && dir != "cache" {
+			files = append(files, filepath.Join(dir, "completions", "_netssh"))
+		}
+	}
+	for _, alias := range aliases {
+		if config.ValidateCommandAlias(alias) != nil || alias == "" {
+			continue
+		}
+		for _, shell := range []string{"bash", "zsh", "fish"} {
+			files = append(files, commandCompletionPath(shell, alias))
+		}
+	}
+	return files
+}
+
+// CompletionAliasState returns the command alias whose completion files were
+// last generated, or "" when there is none.
+func CompletionAliasState() string {
+	data, err := os.ReadFile(filepath.Join(filepath.Dir(AliasesPath()), "completion_alias"))
+	if err != nil {
+		return ""
+	}
+	return strings.TrimSpace(string(data))
+}
+
+// IsGenerated reports whether a completion file was written by netssh,
+// so uninstall never removes a user's own file of the same name.
+func IsGenerated(path string) bool {
+	data, err := os.ReadFile(path)
+	return err == nil && strings.Contains(string(data), "netssh")
+}