Write BEP for full-stack e2e integration test framework

Write the BEP for a full-stack end-to-end integration test framework (all components exercised together). Author it in the backend.ai worktree using the bep-guide skill: reserve a BEP number in proposals/README.md (BEP Number Registry) and draft from proposals/BEP-0000-template.md.\n\nMANDATORY AUTHORING GATE: write the draft in Korean FIRST, get the user review/approval on the Korean draft, and ONLY THEN translate to English and open the PR. Never draft in English first or open the PR before the Korean review.\n\n## Success Criteria\n- [ ] BEP number reserved in proposals/README.md (BEP Number Registry)\n- [ ] Korean draft written first and reviewed/approved by the user before any English\n- [ ] proposals/BEP-XXXX-e2e-integration-test-framework.md drafted from the template (English, post-review)\n- [ ] PR submitted for BEP discussion

JIRA Issue: BA-7034

Read the bep-guide skill, then inspect the BEP Number Registry in proposals/README.md and proposals/BEP-0000-template.md. Reserve a number and write the Korean draft first for user review and approval; only afterward produce the English proposals/BEP-XXXX-e2e-integration-test-framework.md and submit a discussion PR.

Written by the indexing model from the issue text.