fix(ui): port live experience quality updates (#217)

Parse retail PrivateUpdatePropertyInt64 and route authoritative Total/Available Experience through both local-player projections so Attributes, the level meter, and Skills refresh together. Preserve the existing retail XP curve and right-align the Total XP value.

Close the user-confirmed item-give gate for #216 and record the named-retail/ACE/holtburger conformance evidence.

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

src/AcDream.Core.Net/Messages/PrivateUpdatePropertyInt64.cs

@@ -0,0 +1,35 @@
+using System.Buffers.Binary;
+
+namespace AcDream.Core.Net.Messages;
+
+/// <summary>
+/// Inbound retail <c>PrivateUpdatePropertyInt64 (0x02CF)</c>: one signed
+/// 64-bit quality update for the local player. Total Experience (quality 1)
+/// and Available Experience (quality 2) use this message.
+/// </summary>
+/// <remarks>
+/// Retail: <c>CM_Qualities::DispatchUI_PrivateUpdateInt64 @ 0x006AEAD0</c>
+/// reads the sequence byte at +4, property at +5, and value at +9, then calls
+/// <c>ClientObjMaintSystem::Handle_Qualities__PrivateUpdateInt64 @ 0x00559000</c>.
+/// ACE <c>GameMessagePrivateUpdatePropertyInt64</c> and holtburger's
+/// <c>PrivateUpdatePropertyInt64Data</c> confirm the same field order.
+/// </remarks>
+public static class PrivateUpdatePropertyInt64
+{
+    public const uint Opcode = 0x02CFu;
+    public const int BodySize = 17; // opcode(4) + sequence(1) + property(4) + value(8)
+
+    public readonly record struct Parsed(uint Property, long Value);
+
+    /// <summary>Parse a complete 0x02CF body, or return null on mismatch/truncation.</summary>
+    public static Parsed? TryParse(ReadOnlySpan<byte> body)
+    {
+        if (body.Length < BodySize) return null;
+        if (BinaryPrimitives.ReadUInt32LittleEndian(body) != Opcode) return null;
+
+        const int propertyOffset = 5; // opcode + one-byte quality sequence
+        uint property = BinaryPrimitives.ReadUInt32LittleEndian(body[propertyOffset..]);
+        long value = BinaryPrimitives.ReadInt64LittleEndian(body[(propertyOffset + 4)..]);
+        return new Parsed(property, value);
+    }
+}