docs: mirror OpenWA v0.25 sync (webhook events, idempotency header, receipts)
docs: send-as-PDF feature (send_document_pdf, PDF custom fields)
docs: Tier 2 improvements - event log, reactions, DLQ replay, scheduled send, base64 media, media-reply workaround
Add comprehensive wiki pages: Installation, Configuration, Architecture, API Reference, Message Flows, Custom Fields, Troubleshooting, Changelog