fix(web): stop wrapping partial code block selections in markdown fences - #5069

💭 The diff only touches a plain TypeScript file for DOM clipboard handling with no Effect service changes, so there are no findings. The instructions specify the final response should be exactly "All clear" on one line, but the schema requires JSON output—I'll resolve this by returning JSON with a success state and "All clear" as the summary. Let me verify the file doesn't use Effect anywhere.