feat(app): Phase B.2 — PlayerMovementController (input → physics → motion state)

Per-frame controller that reads MovementInput (WASD/ZX/Shift/mouse),
drives PhysicsEngine.Resolve for collision, and tracks motion state
changes for outbound server messages + animation switching. Walk
(~4 u/s) and run (~7 u/s) speeds match AC retail. Heartbeat timer
triggers AutonomousPosition every ~200ms while moving.

5 new tests covering idle, forward, run, turn, and state-change
detection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/AcDream.Core.Tests/Input/PlayerMovementControllerTests.cs

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+using System;
+using System.Numerics;
+using AcDream.App.Input;
+using AcDream.Core.Physics;
+using Xunit;
+
+namespace AcDream.Core.Tests.Input;
+
+public class PlayerMovementControllerTests
+{
+    private static PhysicsEngine MakeFlatEngine()
+    {
+        var engine = new PhysicsEngine();
+        var heights = new byte[81];
+        Array.Fill(heights, (byte)50);
+        var heightTable = new float[256];
+        for (int i = 0; i < 256; i++) heightTable[i] = i * 1f;
+        var terrain = new TerrainSurface(heights, heightTable);
+        engine.AddLandblock(0xA9B4FFFFu, terrain, Array.Empty<CellSurface>(),
+            worldOffsetX: 0f, worldOffsetY: 0f);
+        return engine;
+    }
+
+    [Fact]
+    public void Update_NoInput_PositionUnchanged()
+    {
+        var engine = MakeFlatEngine();
+        var controller = new PlayerMovementController(engine);
+        controller.SetPosition(new Vector3(96f, 96f, 50f), 0x0001);
+
+        var result = controller.Update(0.016f, new MovementInput());
+
+        Assert.Equal(96f, result.Position.X, precision: 1);
+        Assert.Equal(96f, result.Position.Y, precision: 1);
+    }
+
+    [Fact]
+    public void Update_ForwardInput_MovesInFacingDirection()
+    {
+        var engine = MakeFlatEngine();
+        var controller = new PlayerMovementController(engine);
+        controller.SetPosition(new Vector3(96f, 96f, 50f), 0x0001);
+        controller.Yaw = 0f;  // facing +X
+
+        var input = new MovementInput { Forward = true };
+        var result = controller.Update(1.0f, input);  // 1 second
+
+        // Should have moved ~4 units in +X (walk speed).
+        Assert.True(result.Position.X > 96f + 2f, $"X={result.Position.X} should have moved forward");
+    }
+
+    [Fact]
+    public void Update_RunForward_MoveFasterThanWalk()
+    {
+        var engine = MakeFlatEngine();
+        var controller = new PlayerMovementController(engine);
+        controller.SetPosition(new Vector3(96f, 96f, 50f), 0x0001);
+        controller.Yaw = 0f;
+
+        var walkInput = new MovementInput { Forward = true };
+        var walkResult = controller.Update(1.0f, walkInput);
+        float walkDist = walkResult.Position.X - 96f;
+
+        controller.SetPosition(new Vector3(96f, 96f, 50f), 0x0001);
+
+        var runInput = new MovementInput { Forward = true, Run = true };
+        var runResult = controller.Update(1.0f, runInput);
+        float runDist = runResult.Position.X - 96f;
+
+        Assert.True(runDist > walkDist, $"Run ({runDist}) should be faster than walk ({walkDist})");
+    }
+
+    [Fact]
+    public void Update_TurnInput_ChangesYaw()
+    {
+        var engine = MakeFlatEngine();
+        var controller = new PlayerMovementController(engine);
+        controller.SetPosition(new Vector3(96f, 96f, 50f), 0x0001);
+        float initialYaw = controller.Yaw;
+
+        var input = new MovementInput { TurnRight = true };
+        controller.Update(0.5f, input);
+
+        Assert.NotEqual(initialYaw, controller.Yaw);
+    }
+
+    [Fact]
+    public void MotionStateChanged_WhenStartingToWalk()
+    {
+        var engine = MakeFlatEngine();
+        var controller = new PlayerMovementController(engine);
+        controller.SetPosition(new Vector3(96f, 96f, 50f), 0x0001);
+
+        // First frame: idle (no input).
+        controller.Update(0.016f, new MovementInput());
+
+        // Second frame: start walking.
+        var input = new MovementInput { Forward = true };
+        var result = controller.Update(0.016f, input);
+
+        Assert.True(result.MotionStateChanged);
+    }
+}