feat(runtime): define borrowed views commands and ordered events

Establish the J1 presentation-independent contract with instance-scoped clocks and generations, immutable borrowed views, typed generation-gated commands, normalized ordered diagnostics, and teardown acknowledgements. Route graphical startup plus press-time selection, movement, and combat through focused App adapters over the exact existing owners without adding a queue or mirrored world.

Validated by the Release solution build, 13 Runtime tests, 3,838 App tests with three existing skips, and the complete 8,424-test Release suite with five existing skips.

Co-authored-by: Codex <codex@openai.com>

src/AcDream.Runtime/GameRuntimeClock.cs

@@ -0,0 +1,45 @@
+namespace AcDream.Runtime;
+
+public readonly record struct RuntimeFrameTime(
+    ulong FrameNumber,
+    double DeltaSeconds,
+    double SimulationTimeSeconds);
+
+public interface IGameRuntimeClock
+{
+    ulong FrameNumber { get; }
+
+    double SimulationTimeSeconds { get; }
+}
+
+/// <summary>
+/// Instance-scoped simulation clock shared by graphical and future headless
+/// hosts. It owns no wall-clock/global state.
+/// </summary>
+public sealed class GameRuntimeClock : IGameRuntimeClock
+{
+    public ulong FrameNumber { get; private set; }
+
+    public double SimulationTimeSeconds { get; private set; }
+
+    public RuntimeFrameTime Advance(
+        double hostDeltaSeconds,
+        bool advanceSimulationTime = true)
+    {
+        double deltaSeconds = NormalizeDeltaSeconds(hostDeltaSeconds);
+        FrameNumber = checked(FrameNumber + 1UL);
+        if (advanceSimulationTime)
+            SimulationTimeSeconds += deltaSeconds;
+        return new RuntimeFrameTime(
+            FrameNumber,
+            deltaSeconds,
+            SimulationTimeSeconds);
+    }
+
+    public static double NormalizeDeltaSeconds(double deltaSeconds) =>
+        double.IsFinite(deltaSeconds)
+        && deltaSeconds > 0.0
+        && deltaSeconds <= float.MaxValue
+            ? deltaSeconds
+            : 0.0;
+}