[codex] Keep saved conversation opens in saved routes

[katalinawinemixer]

Summary

• Keep open → navigation inside /saved/:runId when a conversation turn is already saved
• Preserve the existing /runs/:runId fallback for unsaved sibling turns
• Add deterministic Playwright coverage for current saved turns, unsaved sibling turns, and saved sibling turns

Why

When viewing a saved trace conversation, clicking open → on a turn always navigated through runPath, which sends the user to /runs/:runId. That kicks users out of the Saved workflow even when the target turn is saved and available under /saved/:runId.

Root cause

RunDetail reused the local conversation viewer across route namespaces, but the ConvoDetail callback hard-coded navigate(runPath(id)). The fix routes saved conversation targets through tracePath("/saved", id) when appropriate, and keeps the runs route as the fallback.

Test plan

• cd app && bun x playwright test tests-e2e/workshop-actions.spec.ts -g "saved conversation"
• cd app && bun x playwright test tests-e2e/workshop-actions.spec.ts
• bun run lint (passes with existing hook warnings, 0 errors)
• bun run build
• git diff --check