fix(ci): avoid duplicate push and pull_request runs

[alexandrelam]

Summary

• restrict push CI runs to main
• keep PR validation on pull_request
• remove the e2e job-level condition that created skipped duplicate statuses on feature-branch pushes

Root cause

The workflow was triggered by both push and pull_request for feature branch updates. On commits attached to an open PR, GitHub created both runs. The e2e job then skipped in the push run because it only allowed PRs or main, which surfaced as an extra skipped check.

Expected effect

PRs should now show only the pull_request checks, while merges to main still run the full push workflow.