ci: extract external E2E into dedicated post-merge workflow

[Copilot]

External runtime E2E was never actually executing. skip-duplicate-actions (same_content_newer) on push: main would mark the run as duplicate of the successful PR CI — which never ran external E2E (run-external-runtime is gated to push+main only). The result: external E2E was permanently skipped.

Root cause is structural: PR validation and post-merge validation have different lifecycles and must not share the same workflow + skip logic.

Summary

main-ci.yml

• Remove push: branches: ["main"] trigger — this workflow now only runs on pull_request and merge_group
• Remove run-external-runtime parameter from web-e2e-run — PR-stage E2E never runs external; defaults to false

post-merge.yml (new)

• Triggered exclusively on push: branches: ["main"]
• Runs dorny/paths-filter with the same external_e2e path set as main-ci.yml
• Calls web-e2e.yml with run-external-runtime: true only when relevant files changed
• cancel-in-progress: false — post-merge jobs should not cancel each other

Screenshots

Before	After
External E2E never executes (always skipped by duplicate-action cache)	External E2E runs on each push to main where external_e2e paths changed

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

From GitHub Copilot