feat(config): add openclaw config validate and improve startup error messages (#31220)

Merged via squash.

Prepared head SHA: 4598f2a541f0bde300a096ef51638408d273c4bd
Co-authored-by: Sid-Qin <201593046+Sid-Qin@users.noreply.github.com>
Co-authored-by: gumadeiras <5599352+gumadeiras@users.noreply.github.com>
Reviewed-by: @gumadeiras

src/cli/program/command-registry.ts

@@ -83,7 +83,7 @@ const coreEntries: CoreCliEntry[] = [
       {
         name: "config",
         description:
-          "Non-interactive config helpers (get/set/unset/file). Default: starts setup wizard.",
+          "Non-interactive config helpers (get/set/unset/file/validate). Default: starts setup wizard.",
         hasSubcommands: true,
       },
     ],