fix: migrate registerHttpHandler to registerHttpRoute (OpenClaw 2026.3.x)

[viewsonic-max]

Problem

api.registerHttpHandler() was removed in OpenClaw 2026.3.x, causing the plugin to fail during registration with:
TypeError: api.registerHttpHandler is not a function

Fix

Migrated to api.registerHttpRoute() with the correct params object signature.

Key details

• auth: 'plugin' is required — omitting it silently prevents the route from mounting (no error, just 404)
• match: 'prefix' supports both POST dispatch and GET WebSub challenge verification at the same path
• No other files needed changes

Before

api.registerHttpHandler(dispatchHandler);

After

api.registerHttpRoute({
  path: '/ax/dispatch',
  handler: dispatchHandler,
  auth: 'plugin',
  match: 'prefix',
});

Tested

Verified on OpenClaw 2026.3.13 — dispatch endpoint responds correctly and agent receives/processes messages end to end.

[madtank]

@viewsonic-max thanks for the PR!