feat(A.5 T13): StreamingController two-tier Tick

Replaces the single-radius Tick with a two-tier model that consumes
StreamingRegion's TwoTierDiff (5-list) and routes to the appropriate
JobKind:

- ToLoadFar    -> _enqueueLoad(id, LoadFar)
- ToLoadNear   -> _enqueueLoad(id, LoadNear)
- ToPromote    -> _enqueueLoad(id, PromoteToNear)
- ToDemote     -> _state.RemoveEntitiesFromLandblock(id) on render thread
- ToUnload     -> _enqueueUnload(id)

Drain switch handles Loaded (terrain + entity layer), Promoted (entity
layer only -- terrain already loaded), Unloaded, Failed, WorkerCrashed.

Constructor signature: nearRadius/farRadius separate ints. Old single-
radius ctor removed; existing single-radius tests updated to pass
nearRadius=farRadius for backward-compat coverage.

GameWindow's enqueueLoad lambda updated from (id =>...) to (id, kind) =>
to match new Action<uint, LandblockStreamJobKind> signature; radius: arg
renamed to nearRadius:/farRadius: (both set to _streamingRadius until T16
wires the full two-tier env-var parsing).

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

src/AcDream.App/Rendering/GameWindow.cs

@@ -1605,14 +1605,13 @@ public sealed class GameWindow : IDisposable
         _streamer.Start();
 
         _streamingController = new AcDream.App.Streaming.StreamingController(
-            // Use a lambda so the Action<uint> delegate matches the method
-            // signature (EnqueueLoad has an optional 'kind' parameter).
-            enqueueLoad: id => _streamer.EnqueueLoad(id, AcDream.App.Streaming.LandblockStreamJobKind.LoadNear),
+            enqueueLoad: (id, kind) => _streamer.EnqueueLoad(id, kind),
             enqueueUnload:    _streamer.EnqueueUnload,
             drainCompletions: _streamer.DrainCompletions,
             applyTerrain:     ApplyLoadedTerrain,
             state:            _worldState,
-            radius:           _streamingRadius,
+            nearRadius:       _streamingRadius,
+            farRadius:        _streamingRadius,
             removeTerrain:    id =>
             {
                 // Phase G.2: release any LightSources attached to entities