feat: add runCommand/useRunCommand for page-triggered commands

[KoSHeroff]

What

Adds runCommand and the useRunCommand() hook so a page can run a Minecraft command, which the mod executes as the player.

import { runCommand, useRunCommand } from '@webgui/react';

runCommand('give @s minecraft:diamond 1');

const run = useRunCommand();
<button onClick={() => run('spawn')}>Teleport to spawn</button>

Fire-and-forget: it posts on the command channel; the mod runs it only when the page is served from a server-declared trusted origin, and drops it otherwise.

Changes

• runCommand(command) util + useRunCommand() hook.
• Tests for runCommand.
• Bump to 1.6.0.

Pairs with the mod PR adding the command channel + trusted-origin enforcement.

Verification

• npm run build succeeds; 32 tests pass.