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>

cmd/netssh/main.go

@@ -41,6 +41,7 @@ var managedSubcommands = map[string]bool{
 	"__complete": true,
 	"help":       true,
 	"version":    true,
+	"uninstall":  true,
 }
 
 func main() {
@@ -357,7 +358,7 @@ func rootCmd() *cobra.Command {
 		},
 	}
 
-	root.AddCommand(notesCmd(), configureCmd(), searchCmd(), cacheCmd(), aliasCmd(), hookCmd(), shellInitCmd(), versionCmd())
+	root.AddCommand(notesCmd(), configureCmd(), searchCmd(), cacheCmd(), aliasCmd(), hookCmd(), shellInitCmd(), versionCmd(), uninstallCmd())
 
 	// cobra builds the "completion" command lazily; force init so we can extend it.
 	root.InitDefaultCompletionCmd()