ci: run external e2e in main ci

[lyzno1]

Summary

• pass run-external-runtime: true from Main CI to the reusable Web Full-Stack E2E workflow
• use PR CI as an explicit external runtime reproduction surface for the current post-merge failure investigation

Verification

• git diff --check
• local external runtime chain: pnpm -C e2e e2e:middleware:up -> pnpm -C e2e e2e:external:prepare -> pnpm -C e2e e2e:external -> pnpm -C e2e e2e:middleware:down passed with 10 scenarios / 159 steps

Notes

• This PR intentionally changes only CI wiring. It does not change E2E assertions or product code.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.36%. Comparing base (eb74946) to head (8be4adb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #38622   +/-   ##
=======================================
  Coverage   85.36%   85.36%           
=======================================
  Files        5022     5022           
  Lines      267188   267188           
  Branches    50848    50848           
=======================================
  Hits       228090   228090           
  Misses      34611    34611           
  Partials     4487     4487           

Flag	Coverage Δ
api	85.63% <ø> (ø)

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