[codex] Open external links in existing window tabs (dev)

[Avesceb]

Summary

Apply the external-link routing fix directly on top of dev, without merging the unrelated commits currently present on main.

• Register Lumen as a viewer for http and https URLs in the generated bundle.
• Prefer an already-open browser scene for incoming external URLs.
• Route each incoming URL through BrowserStore.open, which creates and selects a new tab using the existing URL security policy.

Validation

• swift test on the dev base — 393 tests passed with 0 failures.
• bash -n script/build_and_run.sh
• git diff --check origin/dev...HEAD

Privacy And Security

• This change does not persist, log, expose, or transmit browsing data, credentials, tokens, private-profile data, or sensitive URLs.
• Incoming URLs continue through the existing URL security policy.