feat(mosaic): alphabetize and group mosaic --help output

Enables sortSubcommands on the root program, sessions group, gateway
group, and mission group so all subcommand listings render A-Z. Appends
a Command Groups section via addHelpText to group commands by role
(Runtime, Gateway, Framework, Platform, Runtimes).

Implements CU-04-01, CU-04-02, CU-04-03 from mission cli-unification-20260404.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/mosaic/src/commands/gateway.ts

@@ -30,6 +30,7 @@ export function registerGatewayCommand(program: Command): void {
     .option('-h, --host <host>', 'Gateway host', 'localhost')
     .option('-p, --port <port>', 'Gateway port', '14242')
     .option('-t, --token <token>', 'Admin API token')
+    .configureHelp({ sortSubcommands: true })
     .action(() => {
       gw.outputHelp();
     });