feat(net+ui): Phase G.1 — server time sync + debug controls

WorldSession now surfaces the server's PortalYearTicks via a new
ServerTimeUpdated event, fired from two sources per r12 §12:
  1. Initial ConnectRequest handshake (ConnectRequestServerTime field
     of the optional block — seeds the clock on login).
  2. Every subsequent packet carrying the TimeSync header flag
     (0x01000000) — keeps the client clock within one TimeSync period
     of authoritative server time.

GameWindow subscribes the event into WorldTimeService.SyncFromServer,
so the day/night cycle + keyframe interpolation runs from real server
time in live mode. Offline mode (ACDREAM_LIVE=0) still uses the
seeded-to-noon fallback from OnLoad.

DebugOverlay now exposes sky + weather + lighting state:
  time  0.50  Midsong    (day fraction + hour name)
  wx    Clear parts 0   (weather kind + live particle count)
  lit   1/4            (active / registered lights)

F7 cycles a debug time override through
  (none → midnight → dawn → noon → dusk → none)
F10 cycles weather through
  (Clear → Overcast → Rain → Snow → Storm).

These keybinds satisfy the visual-verification tier so a user can
flip through every state from the running client without touching
the code.

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

src/AcDream.Core.Net/WorldSession.cs

@@ -109,6 +109,21 @@ public sealed class WorldSession : IDisposable
     /// </summary>
     public event Action<HearSpeech.Parsed>? SpeechHeard;
 
+    /// <summary>
+    /// Phase G.1: latest server Portal Year tick count. Seeded from the
+    /// ConnectRequest handshake (r12 §1.3 — server sends absolute game
+    /// time as a double) and refreshed on every TimeSync-flagged packet.
+    /// Subscribers feed this into <c>WorldTimeService.SyncFromServer</c>
+    /// so client-local day/night stays in lockstep with the server clock.
+    /// </summary>
+    public event Action<double>? ServerTimeUpdated;
+
+    /// <summary>
+    /// Latest server tick count from <see cref="ServerTimeUpdated"/>
+    /// events. 0 until the handshake completes.
+    /// </summary>
+    public double LastServerTimeTicks { get; private set; }
+
     /// <summary>
     /// Allow re-sending LoginComplete after a portal teleport. The normal
     /// _loginCompleteSent latch prevents duplicate sends on the initial spawn
@@ -224,6 +239,14 @@ public sealed class WorldSession : IDisposable
 
         // Step 3: seed ISAAC, send ConnectResponse to port+1, with 200ms race delay
         var opt = cr.Optional;
+
+        // Phase G.1: server's initial PortalYearTicks (r12 §1.3) lives
+        // in the ConnectRequest optional section. Publish it to
+        // subscribers so WorldTimeService.SyncFromServer can seed the
+        // client clock.
+        LastServerTimeTicks = opt.ConnectRequestServerTime;
+        ServerTimeUpdated?.Invoke(opt.ConnectRequestServerTime);
+
         byte[] serverSeedBytes = new byte[4];
         BinaryPrimitives.WriteUInt32LittleEndian(serverSeedBytes, opt.ConnectRequestServerSeed);
         byte[] clientSeedBytes = new byte[4];
@@ -393,6 +416,19 @@ public sealed class WorldSession : IDisposable
             SendAck(serverHeader.Sequence);
         }
 
+        // Phase G.1: propagate TimeSync-flagged server time to anyone who
+        // needs it (sky/day-night lerp in particular). Server sends this
+        // periodically — no explicit opcode, just the header flag.
+        if ((serverHeader.Flags & PacketHeaderFlags.TimeSync) != 0)
+        {
+            double t = dec.Packet!.Optional.TimeSync;
+            if (t > 0)
+            {
+                LastServerTimeTicks = t;
+                ServerTimeUpdated?.Invoke(t);
+            }
+        }
+
         foreach (var frag in dec.Packet!.Fragments)
         {
             var body = _assembler.Ingest(frag, out _);