New integration candidates: Elementor, WP Mail SMTP, backup plugins, role editors, Woo Subscriptions

[trueqap]

Highest-value plugins currently without any sensor, given typical hellowp.io client stacks:

1. Elementor — template/global style changes are major content events invisible to ContentSensor diffing (data lives in postmeta `_elementor_data`)
2. WP Mail SMTP — SMTP credential/provider changes explain "mail suddenly broken / mail rerouted" incidents
3. Backup plugins (UpdraftPlus etc.) — especially restore operations, which rewrite the whole site
4. Role editors (User Role Editor, Members) — capability changes are privilege escalation events; core `set_user_role` doesn't catch capability edits within a role
5. WooCommerce Subscriptions — recurring revenue lifecycle (cancel, renewal failure)

Each follows the existing pattern: lazy-load by `class_exists`/`defined` guard + own code block in the catalog.