feat(physics): port retail projectile integration

Add a pure Core projectile driver for retail clock quanta, final-state acceleration, 50-unit velocity clamping, world-space angular integration, full-3D AlignPath, and oriented Setup-local sphere sweeps. Preserve exact success versus set_frame-only failure semantics, independent Contact/OnWalkable state, and full-cell identity across all landblock directions.

Port OBJECTINFO::missile_ignore with explicit weenie/creature metadata, remove the invented transition-step cap, retain PathClipped without arming PerfectClip, and keep authoritative target identity optional. Add malformed-shape/clock, thin-wall, terrain, target-exclusion, frame-spike, failure-state, and boundary conformance coverage.

Retire TS-2 and synchronize the architecture, milestones, roadmap, research oracle, and durable physics memory.

Co-Authored-By: Codex <noreply@openai.com>

src/AcDream.Core/Physics/RetailFrameMath.cs

@@ -0,0 +1,63 @@
+using System.Numerics;
+
+namespace AcDream.Core.Physics;
+
+/// <summary>
+/// Retail frame-orientation helpers used by physics presentation.
+/// </summary>
+public static class RetailFrameMath
+{
+    /// <summary>
+    /// Points the frame's local +Y axis along a world-space direction with
+    /// zero roll. This is the observable contract of retail
+    /// <c>Frame::set_vector_heading</c> at <c>0x00535DB0</c>: normalize the
+    /// full three-dimensional vector, derive compass yaw plus elevation, and
+    /// replace the frame rotation. A zero-length vector leaves the prior
+    /// orientation unchanged.
+    /// </summary>
+    public static Quaternion SetVectorHeading(
+        Quaternion currentOrientation,
+        Vector3 direction)
+    {
+        float lengthSquared = direction.LengthSquared();
+        if (lengthSquared < PhysicsGlobals.EpsilonSq || !float.IsFinite(lengthSquared))
+            return currentOrientation;
+
+        Vector3 forward = direction / MathF.Sqrt(lengthSquared);
+
+        // Retail's zero-roll Euler construction is equivalent to choosing a
+        // horizontal right axis from the compass heading, then deriving the
+        // remaining up axis. At a perfectly vertical heading atan2(0, 0)
+        // resolves to zero, so retain +X as the deterministic right axis.
+        Vector3 right;
+        if (forward.X == 0f && forward.Y == 0f)
+        {
+            right = Vector3.UnitX;
+        }
+        else
+        {
+            // Normalize the horizontal pair without squaring the original
+            // components. That preserves every non-zero compass component,
+            // including a nearly vertical vector below PhysicsGlobals.EPSILON,
+            // just as retail's atan2-based construction does.
+            float scale = MathF.Max(MathF.Abs(forward.X), MathF.Abs(forward.Y));
+            float x = forward.X / scale;
+            float y = forward.Y / scale;
+            float horizontalLength = MathF.Sqrt((x * x) + (y * y));
+            right = new Vector3(y / horizontalLength, -x / horizontalLength, 0f);
+        }
+
+        Vector3 up = Vector3.Normalize(Vector3.Cross(right, forward));
+
+        // System.Numerics uses row-vector transforms. Each row below is the
+        // world direction of one local basis axis: +X right, +Y heading,
+        // +Z up.
+        var rotation = new Matrix4x4(
+            right.X,   right.Y,   right.Z,   0f,
+            forward.X, forward.Y, forward.Z, 0f,
+            up.X,      up.Y,      up.Z,      0f,
+            0f,        0f,        0f,        1f);
+
+        return Quaternion.Normalize(Quaternion.CreateFromRotationMatrix(rotation));
+    }
+}