Refactor project structure and update documentation. Replace PixiJS with plain DOM for UI rendering, enhance README with game features, and revise protocol documentation for HTTP API. Remove unused files and streamline client code for better maintainability.

src/HSchool.Simulation/GameClock.cs

@@ -0,0 +1,67 @@
+namespace HSchool.Simulation;
+
+/// <summary>
+/// In-game calendar of one school. Time only moves while <see cref="IsRunning"/> is set, and it
+/// moves by whole fixed steps — never by wall-clock deltas — so the same tick count always
+/// produces the same date.
+/// </summary>
+public sealed class GameClock
+{
+    /// <summary>Earliest date a school may start at; anything below is a typo, not a design choice.</summary>
+    public static readonly DateTime MinStartDate = new(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+
+    public static readonly DateTime MaxStartDate = new(2999, 12, 31, 23, 59, 59, DateTimeKind.Utc);
+
+    private int _speedIndex = ClockSpeed.DefaultIndex;
+
+    public GameClock(DateTime startDate)
+    {
+        if (!IsValidStartDate(startDate))
+        {
+            throw new ArgumentOutOfRangeException(nameof(startDate), startDate, "Start date is outside the supported range.");
+        }
+
+        // The game calendar is not tied to a real time zone; UTC keeps serialization unambiguous.
+        Time = DateTime.SpecifyKind(startDate, DateTimeKind.Utc);
+    }
+
+    public DateTime Time { get; private set; }
+
+    /// <summary>
+    /// Schools live on their own: a new calendar starts running and only the player's pause
+    /// button stops it. Leaving for the menu does not.
+    /// </summary>
+    public bool IsRunning { get; set; } = true;
+
+    /// <summary>Index into <see cref="ClockSpeed.Multipliers"/>; invalid values are ignored.</summary>
+    public int SpeedIndex
+    {
+        get => _speedIndex;
+        set
+        {
+            if (ClockSpeed.IsValid(value))
+            {
+                _speedIndex = value;
+            }
+        }
+    }
+
+    public double Multiplier => ClockSpeed.MultiplierAt(_speedIndex);
+
+    public static bool IsValidStartDate(DateTime date) => date >= MinStartDate && date <= MaxStartDate;
+
+    /// <summary>
+    /// Advances the calendar by one fixed step of <paramref name="realSeconds"/>, scaled by the
+    /// base rate and the current speed. Does nothing while paused.
+    /// </summary>
+    public void Advance(double realSeconds, double gameMinutesPerRealSecond)
+    {
+        if (!IsRunning)
+        {
+            return;
+        }
+
+        var gameMinutes = realSeconds * gameMinutesPerRealSecond * Multiplier;
+        Time = Time.AddMinutes(gameMinutes);
+    }
+}