Add component identity to the /status self-report payload

[tomasstark]

This PR adds a self-describing component: { kind: "php-sdk", version } to the /.well-known/supertab/status payload — the PHP counterpart of getsupertab/connect-sdk-typescript#40.

Context

The status payload reported only sdkVersion, which tells the backend nothing about which package a deployment actually updates from. The backend's per-component version resolver (laterpay/supertab-connect#1094) maps component.kind to the right registry and label; a bare sdkVersion payload gets legacy-shimmed to ts-sdk and checked against npm — the wrong registry for a Packagist-installed PHP deployment. (The WordPress plugin builds its own status payload with kind: "wordpress-plugin" — getsupertab/connect-wp#18 — so this field covers standalone PHP deployments and the plain-permalink WP fallback where the SDK answers the probe itself.)

Key Changes

• handleStatusRequest() now emits component: { kind: "php-sdk", version: HttpClient::resolveVersion() } alongside the unchanged sdkVersion.
• Test asserting the component identity and that its version matches sdkVersion; README payload example updated.

Additive and backward-compatible — older backends ignore the new field, and the backend degrades unknown kinds to "show version, no nudge" until it wires a php-sdk resolver. No version bump or release here; that stays a separate step.