fix(app): route legacy drafts to session page

[Hona]

Summary

• redirect draft URLs to the existing directory session route when redesigned layouts are disabled
• keep redesigned drafts on the standalone new-session route
• cover the legacy redirect, titlebar shell, and prompt rendering with Playwright

Fixes#35701

Tests

• bun typecheck
• bun run test:e2e -- e2e/regression/legacy-new-session.spec.ts e2e/regression/new-session-panel-corner.spec.ts --project=chromium --workers=1

[Copilot]

Pull request overview

This PR ensures draft URLs (/new-session?draftId=...) behave correctly when the redesigned layouts are disabled by redirecting them to the existing legacy directory session route, while keeping the redesigned draft flow unchanged when the new layouts are enabled.

Changes:

• Add a conditional redirect in DraftRoute to send legacy-layout users from /new-session?draftId=... to /:dir/session.
• Add a Playwright regression test covering the legacy redirect and key UI affordances (titlebar drag region + prompt input) after navigation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/app/src/app.tsx	Routes draft URLs to the legacy directory session page when newLayoutDesigns is disabled; otherwise continues rendering the redesigned draft route.
packages/app/e2e/regression/legacy-new-session.spec.ts	Adds an E2E regression test verifying the redirect to the legacy session route and basic shell/prompt rendering.

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