fix(app): keep session routes within layouts

[Brendonovich]

Summary

• register the settings command in the persistent new layout so cmd+, remains available on session error pages
• match target-session URLs inside the active legacy or new layout so server-scoped content always mounts
• resolve legacy target sessions through the URL-selected server and replace the history entry when redirecting

Validation

• bun typecheck in packages/app
• bun run test:unit in packages/app (545 passed)
• bun turbo typecheck (30 packages passed)