refactor(app): remove V1 client compatibility - #43045

Summary

• keep only canonical GUI routes: /, /new-session, and /server/:serverKey/session/:id
• remove V1 storage aliases, generic legacy migration, Tauri import, old layout onboarding IPC, /global/health, and dead Desktop shims
• make App E2E mocks and timeline fixtures use direct OpenCodeEvent and SessionMessageInfo contracts
• remove tests that only covered unsupported V1 or old Desktop runtime behavior
• relocate proven V2 server, layout, permission, prompt, draft-store, and workspace-path state once into canonical storage
• preserve the shipped hidden Linux launcher used by existing GNOME/KDE pins

Architecture

• keeps multi-server identity as (server key, Session ID)
• schema-decodes timeline events and messages against current server schemas
• keeps read-once V2 relocation separate from removed V1/Tauri compatibility
• preserves the production event/transcript adapter for the next session-model PR
• does not change Core, Server, Protocol, Client, Schema, or generated surfaces

Testing

• bun typecheck in packages/app, packages/desktop, and packages/ui
• bun run typecheck:e2e in packages/app
• 679 App unit tests, 43 App browser tests, 71 Desktop tests, and 27 UI tests
• 97 App Playwright E2E tests plus focused remote permission coverage
• 37 production-build timeline stability Playwright tests
• current event and message schema validation fixture tests
• App and Desktop production builds
• bun install --frozen-lockfile with Bun 1.3.14
• repository pre-push typecheck