fix(A.5 T16): debug overlay shows _nearRadius instead of legacy _streamingRadius

Cosmetic follow-up flagged by spec compliance review on T13-T16 bundle
(commits fb10c3f / aff35d2 / b8d80fe / c4fd373). The debug overlay's
getStreamingRadius callback was reading _streamingRadius — the legacy
single-tier field that's only updated by ACDREAM_STREAM_RADIUS. Operators
using the new ACDREAM_NEAR_RADIUS / ACDREAM_FAR_RADIUS env vars would
see the overlay frozen at the default 2.

Switch to _nearRadius. The overlay still shows a single number (matching
its label "Streaming radius"); operators who want both tier numbers can
read the launch log.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -1151,7 +1151,8 @@ public sealed class GameWindow : IDisposable
                     getNearestObjLabel:   () => _lastNearestObjLabel,
                     getColliding:         () => _lastColliding,
                     getDebugWireframes:   () => _debugCollisionVisible,
-                    getStreamingRadius:   () => _streamingRadius,
+                    getStreamingRadius:   () => _nearRadius,   // A.5 T16 follow-up: was _streamingRadius (legacy single-tier); show near tier
+
                     getMouseSensitivity:  () => GetActiveSensitivity(),
                     getChaseDistance:     () => _chaseCamera?.Distance ?? 0f,
                     getRmbOrbit:          () => _rmbHeld,