v1.13.0

Add PayPal Redirect payment mode to Membership Form settings

New payment mode on Settings → Membership Form: after submit the member sees the confirmation message plus a pulsing REDIRECTING FOR PAYMENT banner, then is redirected to a configurable PayPal URL after an adjustable delay (1–60s, default 5s). The redirect URL supports {amount}, {email}, {first_name}, {last_name}, {address}, and {home_id} placeholders (URL-encoded), with a no-JS fallback link.

Bump version to 1.13.0.

https://claude.ai/code/session_01MQaWK1oZnrX9GjowrBy4Fs

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Merged from #37 by @sfxdotcom.