Add camera AR view, GPS stable mode and wider machine range

- Real-world mode opens the phone's rear camera as the game background;
  the 3D camera stands at the GPS position and follows the phone's
  orientation, so machines, beacons, range circles, the route and the
  robot appear in their real direction. City, traffic and family are
  hidden in this view; a toggle switches back to the 3D map, and drag
  turns the view where there is no orientation sensor
- Stable mode (default on): drops GPS jumps impossible on foot, holds the
  position until it drifts past half the GPS error, calms the compass
- Arrival range is 2.5x the GPS error (20–50 m), shown as a ground circle
- Tests for the stabilizer, AR orientation and field of view

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/realworld.js

@@ -16,15 +16,44 @@ export function smoothFix(previous, fix) {
     return {x, z, accuracy, time: fix.time, speed: fix.speed ?? Math.hypot(x - previous.x, z - previous.z) / dt};
 }
 
-// How close counts as "at the machine": twice the GPS error, between 12 m (good outdoor fix) and 40 m.
-export const arrivalRadius = accuracy => Math.min(40, Math.max(12, accuracy * 2));
+// Stable mode on top of smoothFix, against phone GPS jitter:
+//  - a fix further from the estimate than both errors plus a brisk walk allows is a jump and is
+//    dropped (after three in a row it is accepted: the phone really moved, e.g. got in a car);
+//  - the shown position stays put until the estimate drifts beyond about half the GPS error,
+//    or the phone reports walking speed. Without stable mode every smoothed fix is shown.
+export function createStabilizer({maxSpeed = 3} = {}) {
+    let estimate = null, shown = null, rejected = 0;
+    return {
+        stable: true,
+        push(fix) {
+            if (estimate && this.stable && fix.time - estimate.time < 30000) {
+                const dt = Math.max(.001, (fix.time - estimate.time) / 1000);
+                const reach = estimate.accuracy + fix.accuracy + maxSpeed * dt * 1.5;
+                if (Math.hypot(fix.x - estimate.x, fix.z - estimate.z) > reach && fix.accuracy > estimate.accuracy / 2 && rejected < 3) {
+                    rejected++;
+                    return shown && {...shown};
+                }
+            }
+            rejected = 0;
+            estimate = smoothFix(estimate, fix);
+            const drift = shown ? Math.hypot(estimate.x - shown.x, estimate.z - shown.z) : Infinity;
+            if (!this.stable || drift > Math.max(3, estimate.accuracy / 2) || (fix.speed ?? 0) > .7) shown = {...estimate};
+            else shown = {...shown, accuracy: estimate.accuracy, time: estimate.time, speed: fix.speed ?? 0};
+            return {...shown};
+        }
+    };
+}
+
+// How close counts as "at the machine": 2.5× the GPS error, between 20 m (good outdoor fix) and 50 m,
+// so reaching the area around a machine is enough.
+export const arrivalRadius = accuracy => Math.min(50, Math.max(20, accuracy * 2.5));
 
 export const insideWorld = (bounds, x, z) => x > bounds.minX && x < bounds.maxX && z > bounds.minZ && z < bounds.maxZ;
 
 // Watches the phone's position and compass. Calls onFix({x, z, accuracy, speed, lat, lon}),
 // onHeading(radians in the game's heading convention), onError(message) for a real problem and
-// onStatus(message) while it is still searching.
-export function startTracking({onFix, onHeading, onError, onStatus = () => {}}) {
+// onStatus(message) while it is still searching. `stabilizer` filters the fixes (see above).
+export function startTracking({onFix, onHeading, onError, onStatus = () => {}, stabilizer = createStabilizer()}) {
     if (!('geolocation' in navigator)) {
         onError('این دستگاه موقعیت‌یابی (GPS) ندارد.');
         return () => {};
@@ -33,12 +62,12 @@ export function startTracking({onFix, onHeading, onError, onStatus = () => {}})
         onError('موقعیت‌یابی فقط روی HTTPS کار می‌کند؛ بازی را از نشانی https:// باز کنید.');
         return () => {};
     }
-    let estimate = null, fixes = 0;
+    let fixes = 0;
     const handle = position => {
         const {latitude: lat, longitude: lon, accuracy, speed} = position.coords, local = toLocal(lat, lon);
-        estimate = smoothFix(estimate, {...local, accuracy: Math.max(3, accuracy), speed: Number.isFinite(speed) ? speed : null, time: position.timestamp});
+        const shown = stabilizer.push({...local, accuracy: Math.max(3, accuracy), speed: Number.isFinite(speed) ? speed : null, time: position.timestamp});
         fixes++;
-        onFix({...estimate, lat, lon});
+        if (shown) onFix({...shown, lat, lon});
     };
     const fail = error => {
         if (error.code === error.PERMISSION_DENIED) onError('اجازهٔ دسترسی به موقعیت داده نشد. در تنظیمات مرورگر و گوشی، Location را برای این سایت مجاز کنید. (کد ۱)');