Add preview testing system for action changes (#178)

* add preview testing system for action changes

- add preview-create.yml workflow (on PR open with action/ changes)
- add preview-cleanup.yml workflow (on PR close)
- add preview-create.ts script (creates repo, copies secrets, posts comment)
- add preview-cleanup.ts script (deletes preview repo)
- add wiki/preview-repo.md documentation
- add libsodium-wrappers for secret encryption

* fix: use --ignore-scripts for preview CI to avoid prisma generate

* fix: skip postinstall scripts in preview workflows

* fix: use fake DATABASE_URL for prisma generate

* remove @pullfrog mention from PR comment to avoid triggering

* add Vercel automation bypass for preview webhook forwarding

* replace fixed delay with exponential backoff polling for repo readiness

* chore: trigger preview redeploy for env var

* chore: trigger preview redeploy

* fix: skip webhook forwarding in non-production to prevent loops

README.md

@@ -1,3 +1,4 @@
+<!-- test preview system -->
 <p align="center">  
   <h1 align="center">
     <picture>