Implement tiled multiplayer city simulation and scaling stages

tools/README.md

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+# Offline tools
+
+City generation stays in TypeScript. `npm run cli` generates a world from OSM;
+`npm run export-city -- world.json public/cities/demo` publishes its tiled form.
+
+Exports are immutable: choose a new directory for a new city revision. Each
+export contains a versioned manifest, gzip tiles with SHA-256 hashes and a
+compact navigation index. Buildings are repeated whole at tile boundaries;
+clients deduplicate IDs. Geometry extending outside the chosen OSM bbox does
+not create tiles outside the city.
+
+`generate-worker.ts` implements the isolated server job: fetch OSM, generate,
+export into an unpublished staging folder, then rename it into the catalogue.
+`rust.mjs` provides npm entry points for Cargo without changing the system PATH.