When the user approves the visual companion, open their browser automatically the
first time a screen is actually ready to show — rather than at startup (just the
waiting page) or making them open the URL by hand.
Opt-in and gated on approval: off unless BRAINSTORM_OPEN is set (start-server.sh
--open, which the agent passes only after the user agrees to use the companion).
Even then it fires once, and is skipped if a browser is already connected, on a
non-loopback/remote bind, or when headless. Launcher is the platform default
(open / xdg-open / WSL cmd.exe) or BRAINSTORM_OPEN_CMD; best-effort, never fatal.
lifecycle.test.js: opens once on the first screen when approved; does NOT open
without approval.
Closes#755
Refs #759
463dfb7fd4