openai/gpt-chat-latest → B (3:2)

Side B makes functional improvements to the development workflow by adding a persistent `fixture-data/` setup, reusing seeded data across runs, preferring a stable port with fallback, launching via `cargo watch`, and extending server startup handling, all of which directly improve ongoing developer iteration. Side A mostly introduces a large planning document plus a thin `RouteContext` wrapper around `ThreadNav` with re-exports, which establishes direction but contributes relatively little executable behavior beyond API scaffolding.