feat: App-Gerüst mit Spieler auf Testfläche

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/world/coords.js

@@ -0,0 +1,27 @@
+export const TILE_PX = 256;
+export const WORLD_HALF = 16384;      // gtadb-Weltgrenze in Metern
+export const CHUNK_SIZE = 250;
+export const SLICE = { x0: -1000, x1: 2000, y0: -500, y1: 2500 };
+export const CHUNKS_PER_SIDE = (SLICE.x1 - SLICE.x0) / CHUNK_SIZE;   // 12
+
+export const worldToThree = (X, Y) => ({ x: X, z: -Y });
+export const threeToWorld = (x, z) => ({ X: x, Y: -z });
+
+export function tileForWorld(X, Y) {
+    return {
+        row: Math.floor((WORLD_HALF - Y) / TILE_PX),
+        col: Math.floor((X + WORLD_HALF) / TILE_PX),
+    };
+}
+
+export function chunkForWorld(X, Y) {
+    return {
+        i: Math.floor((X - SLICE.x0) / CHUNK_SIZE),
+        j: Math.floor((SLICE.y1 - Y) / CHUNK_SIZE),
+    };
+}
+
+/** Nordwest-Ecke eines Chunks in Weltkoordinaten. */
+export function chunkOrigin(i, j) {
+    return { X: SLICE.x0 + i * CHUNK_SIZE, Y: SLICE.y1 - j * CHUNK_SIZE };
+}