viewer: slow first-person walk/run/jump speeds

Walk 4→2 m/s, run 5.5→5 m/s, jump 6→5 (~1.27 m peak). Applied to both
the GLB walkthrough controller (viewer) and the editor first-person
controls so the two surfaces stay consistent.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/viewer/src/components/viewer/glb-walkthrough-controller.tsx

@@ -410,10 +410,10 @@ export function GlbWalkthroughController({ url }: { url: string }) {
         floatSensorRadius={0.15}
         floatSpringK={1200}
         gravity={9.81}
-        jumpVel={6}
-        maxRunSpeed={5.5}
+        jumpVel={5}
+        maxRunSpeed={5}
         maxSlope={1.2}
-        maxWalkSpeed={4}
+        maxWalkSpeed={2}
         position={start.position}
         ref={setControllerApi}
       />