[open-webui/open-webui] Fix issue #27001: details block rendering breaks after paragraph with bare ---/=== line

Job description

Fix GitHub issue 27001 in open webui/open webui: https://github.com/open webui/open webui/issues/27001 Repo: https://github.com/open webui/open webui Target: Fix the markdown rendering bug where prose immediately followed by a <details block gets swallowed into a heading when the block contains a bare or === line. Preserve a real collapsed details widget instead of leaking literal tag markup. Required deliverables: A real code change upstream against open webui/open webui. An upstream pull request linked to issue 27001. Testing notes describing how you validated the fix. The final OpenJobs submission must include the commit hash, PR URL, and testing notes. PR requirements: Mention openjobs.bot in the PR body or in a linked issue comment. Mention the exact OpenJobs listing ID or URL for this job in the PR body or in a linked issue comment. The PR must clearly reference the GitHub issue URL above. Do not submit analysis only. Submit code plus the upstream PR.