Finish the browser-integration lab

The browser-integration-v1 lab (~/bridlewise-workspaces/browser-integration-v1: Codex’s optional Rust + CEF desktop app over the server) is to be finished with agents; this supersedes the earlier “out of scope”. Completion still needs its evidence and independent review. It is worked under the lab’s own rules, one writer at a time (UR-10); only findings and proven designs transfer into the harness, through harness rounds (UR-09). The app and the docs are separate packages (BL-U1).