feat(spells): Phase E.5 CastSpellRequest + Spellbook/enchantment state

Completes the client-side spell loop on top of Phase F.1. Player can
send cast requests; spellbook + active-enchantment state mirrors what
the server broadcasts.

Wire layer:
- CastSpellRequest (C→S, inside 0xF7B1 GameAction):
  - BuildUntargeted (0x0048): self-buffs, recalls, heal-self — 16 bytes.
  - BuildTargeted (0x004A): projectile attacks, target buffs/debuffs — 20 bytes.
- GameEvents parsers added:
  - 0x02C1 MagicUpdateSpell: spell-id → spellbook.
  - 0x01A8 MagicRemoveSpell.
  - 0x02C2 MagicUpdateEnchantment: spellId + layerId + duration + casterGuid
    (summary head; full stat-mod body deferred).
  - 0x02C3 MagicRemoveEnchantment: (layerId, spellId).
  - 0x02C7 MagicDispelEnchantment: same shape.

Core layer:
- Spellbook: learned-spell set + active-enchantment-by-layer dict
  with events (SpellLearned, SpellForgotten, EnchantmentAdded,
  EnchantmentRemoved). Duplicate learn is idempotent. Same-layer
  add refreshes duration. Purge fires per-record remove for UI
  cleanup.
- ActiveEnchantmentRecord: (SpellId, LayerId, Duration, CasterGuid).

Tests (10 new):
- CastSpellRequest untargeted (16 bytes) + targeted (20 bytes) wire encoding.
- GameEvents: MagicUpdateSpell, MagicUpdateEnchantment,
  MagicRemoveEnchantment round-trip.
- Spellbook: learn idempotent, forget, add/refresh enchantment,
  remove fires event, purge-all clears + fires per-record.

Build green, 555 tests pass (up from 544).

Ref: r01 §2 (wire casts), §3 (cast state machine), §5 (stacking rules).
Ref: r08 §3 opcodes 0x0048/0x004A, §4 opcodes 0x01A8/0x02C1-0x02C8.

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

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

@@ -264,6 +264,63 @@ public static class GameEvents
             BinaryPrimitives.ReadUInt32LittleEndian(payload.Slice(4)));
     }
 
+    // ── Spell enchantments ──────────────────────────────────────────────────
+
+    /// <summary>
+    /// 0x02C3 MagicRemoveEnchantment — (layerId, spellId).
+    /// </summary>
+    public readonly record struct MagicRemoveEnchantment(uint LayerId, uint SpellId);
+
+    public static MagicRemoveEnchantment? ParseMagicRemoveEnchantment(ReadOnlySpan<byte> payload)
+    {
+        if (payload.Length < 8) return null;
+        return new MagicRemoveEnchantment(
+            BinaryPrimitives.ReadUInt32LittleEndian(payload),
+            BinaryPrimitives.ReadUInt32LittleEndian(payload.Slice(4)));
+    }
+
+    /// <summary>0x01A8 MagicRemoveSpell — spell id removed from spellbook.</summary>
+    public static uint? ParseMagicRemoveSpell(ReadOnlySpan<byte> payload)
+    {
+        if (payload.Length < 4) return null;
+        return BinaryPrimitives.ReadUInt32LittleEndian(payload);
+    }
+
+    /// <summary>
+    /// 0x02C2 MagicUpdateEnchantment — the Enchantment blob. Full layout
+    /// (ACE <c>Enchantment.Pack</c>) is ~80+ bytes of spell metadata +
+    /// stat mods. We expose the first few fields that drive the enchant
+    /// bar UI; the rest is available via the raw payload view.
+    /// </summary>
+    public readonly record struct EnchantmentSummary(
+        uint SpellId,
+        uint LayerId,
+        float Duration,
+        uint CasterGuid);
+
+    public static EnchantmentSummary? ParseMagicUpdateEnchantment(ReadOnlySpan<byte> payload)
+    {
+        // Layout (ACE Enchantment.Pack):
+        //   u32 spellId
+        //   u32 layerId
+        //   f32 duration
+        //   u32 casterGuid
+        //   ... (stat mods, category, power, etc.)
+        if (payload.Length < 16) return null;
+        return new EnchantmentSummary(
+            BinaryPrimitives.ReadUInt32LittleEndian(payload),
+            BinaryPrimitives.ReadUInt32LittleEndian(payload.Slice(4)),
+            BinaryPrimitives.ReadSingleLittleEndian(payload.Slice(8)),
+            BinaryPrimitives.ReadUInt32LittleEndian(payload.Slice(12)));
+    }
+
+    /// <summary>
+    /// 0x02C7 MagicDispelEnchantment — (layerId, spellId).
+    /// Structure matches MagicRemoveEnchantment.
+    /// </summary>
+    public static MagicRemoveEnchantment? ParseMagicDispelEnchantment(ReadOnlySpan<byte> payload)
+        => ParseMagicRemoveEnchantment(payload);
+
     // ── Appraise / identify ─────────────────────────────────────────────────
 
     /// <summary>0x00C9 IdentifyObjectResponse header.</summary>