fix(cli): exit 0 when invoking parent commands without a subcommand (#73077)

Several `openclaw <parent>` commands (channels, plugins, approvals, devices,
cron, mcp) were exiting with code 1 when invoked bare, while printing the
same help-style content that `<parent> --help` produces (which exits 0).
This broke `&&` chains and surfaced a misleading
`ELIFECYCLE Command failed with exit code 1.` line under pnpm.

Add a small `applyParentDefaultHelpAction(cmd)` helper in
`src/cli/program/parent-default-help.ts` that attaches a default action
which prints the parent's own help and sets `process.exitCode = 0`. The
helper is a no-op when the parent already has its own action (e.g.
`agents` defaulting to `agents list`), so existing intentional defaults
are preserved.

Apply it to the six core parents listed in #73077.

extensions/memory-core/src/cli.ts

@@ -219,4 +219,9 @@ export function registerMemoryCli(program: Command) {
     .action(async (opts: MemoryRemBackfillOptions) => {
       await runMemoryRemBackfill(opts);
     });
+
+  memory.action(() => {
+    memory.outputHelp();
+    process.exitCode = 0;
+  });
 }