Pierre-Yves

Following the builder pattern, provide a new `CityBuilder` facility accessible from the WASM interface. ## Proposed interface ```rust let mut city_generator = CityGeneratorBuilder::new() .set_map_generator_options(/* ... */) .set_simulation_rng_seed(123456) .build()?; let map1...

Original design: Must at least work in the storybooks.

Upgraded to Next.js v16 to use Turbopack instead of Webpack (WasmPackPlugin no longer maintained).