chore: wire local shared header bridge setup

[vitormattos]

Summary

• load local fragment webhook environment variables from the root Makefile
• keep LibreSign/SaaS-specific WordPress overrides in this repository
• add a SaaS-local nginx override for large fragment webhook payloads
• wait for the static site local build to finish before recreating the site nginx container
• update the site and wordpress-docker submodule pointers for the header bridge implementation

Why

The static site 404s were caused by the SaaS orchestration flow exposing nginx before the local static build was ready. The final fix keeps the original site docker/nginx configuration intact and corrects the startup sequencing in the root Makefile.

Validation

• make up site produces a ready local static build before nginx is recreated
• http://localhost:8081/, /faq, and /features respond with HTTP 200
• local WordPress still renders the shared header and footer fragments after publishing