[codex] Add embedded sidebar workspace tabs

[Sebeb]

Summary

• Adds embedded workspace tab controls to the sidebar workspace experience
• Adds sidebar view state, settings persistence, translations, and focused store tests
• Rebases the branch to remove unrelated old-main changes from the PR scope

Validation

• Branch review agent ran focused tests plus repo typecheck/lint/format before the rebase
• Rebased onto origin/main and verified the final diff scope