fix(ui): night-round review — F3/F4/F7 cast-button tooltip strings

F3: TS-85 had claimed the plain-spell branch's three SetTooltip format
strings were "genuine gmNoticeHandler vtable SLOTS" and unrecoverable
from the decomp dump. That was itself the artifact — Binary Ninja's
pseudo-C rendering of PStringBase::sprintf's second argument as
"&gmSpellcastingUI::`vftable'.RecvNotice_XXX" was a spurious symbol
match, not the true operand. A direct capstone disassembly of the raw
bytes at gmSpellcastingUI::UpdateCastButtonTooltip @0x004c6a30's four
call sites (0x4c6e48/0x4c6ea4/0x4c6f18/0x4c6f5d) resolves the actual
pushed literals: "CAST %hs" @0x7b63a4 (untargeted/self-cast, and
targeted+compatible with " on %s" @0x7b6464 appended), "You must
select an appropriate target for %hs" @0x7b6348 (incompatible target),
"You must select a target for %hs" @0x7b63b8 (no target). %hs is the
spell's own name throughout.

Added RuntimeSpellCastState.EvaluateCastGate (SpellCastGate: NoTarget-
Needed/TargetCompatible/TargetIncompatible/NoTargetSelected/Unknown),
refactoring IsTargetReady to use it, and wired
SpellcastingUiController.ComputeSpellCastState to the four-state
tooltip text, replacing the bare-spell-name fallback.

F4: the endowment branch's "USE the %s" (and both select-target
strings) vararg is NOT the bare item name — retail composes
"%s (%hs)" @0x7b64d8 (item name, spell name) once at @0x004c6bb6-ef
and reuses it for all three format strings, byte-confirmed by all
three sprintf call sites (0x4c6c7f/0x4c6ca4/0x4c6d46) reading the
identical stack slot. Added ComposeEndowmentName and wired it in place
of the bare item name.

F7: added test coverage for the two genuinely NEW disabled states
(needs-target, needs-appropriate-target) neither branch had any
coverage for before, plus the enabled untargeted/targeted-compatible
states and both endowment-branch composed-name cases.

Corrected the register's TS-85 row (the "cannot be recovered" claim
and the endowment operand claim) with the byte-decoded findings.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.Runtime/Gameplay/RuntimeSpellCastState.cs

@@ -50,18 +50,34 @@ public sealed class RuntimeSpellCastState
     public uint? LastRequestedTargetId { get; private set; }
     public event Action? StateChanged;
 
-    public bool IsTargetReady(uint spellId)
+    public bool IsTargetReady(uint spellId) =>
+        EvaluateCastGate(spellId)
+            is SpellCastGate.NoTargetNeeded or SpellCastGate.TargetCompatible;
+
+    /// <summary>
+    /// <c>gmSpellcastingUI::UpdateCastButtonTooltip @0x004c6a30</c>'s
+    /// plain-spell branch (<c>m_endowmentItemID == 0</c>) gate, split out
+    /// (night-round review F3) so the tooltip presenter can distinguish
+    /// retail's four states rather than just the enabled/disabled boolean
+    /// <see cref="IsTargetReady"/> collapses them to. Byte-decoded call
+    /// sites: the untargeted/self-cast branch at <c>0x4c6f35</c>, the
+    /// targeted-and-compatible branch at <c>0x4c6e57</c>
+    /// (<c>ClientMagicSystem::ObjectCompatibleWithSpell @0x567c30</c>), and
+    /// the two disabled tails at <c>0x4c6f04</c> (incompatible) and
+    /// <c>0x4c6e2b</c> (nothing selected).
+    /// </summary>
+    public SpellCastGate EvaluateCastGate(uint spellId)
     {
         if (!_spellbook.Knows(spellId)
             || !_spellbook.TryGetMetadata(spellId, out SpellMetadata spell))
-            return false;
+            return SpellCastGate.Unknown;
         if (spell.IsSelfTargeted || spell.IsUntargeted || spell.TargetMask == 0u)
-            return true;
-        return _selection.SelectedObjectId is uint target and not 0u
-            && _operations.IsTargetCompatible(
-                target,
-                spell,
-                showMessage: false);
+            return SpellCastGate.NoTargetNeeded;
+        if (_selection.SelectedObjectId is not (uint target and not 0u))
+            return SpellCastGate.NoTargetSelected;
+        return _operations.IsTargetCompatible(target, spell, showMessage: false)
+            ? SpellCastGate.TargetCompatible
+            : SpellCastGate.TargetIncompatible;
     }
 
     public CastRequestResult Cast(uint spellId)
@@ -159,3 +175,27 @@ public enum CastRequestResult
     MissingComponents,
     Unavailable,
 }
+
+/// <summary>
+/// The four retail cast-button states <c>gmSpellcastingUI::
+/// UpdateCastButtonTooltip @0x004c6a30</c>'s plain-spell branch
+/// distinguishes — see <see cref="RuntimeSpellCastState.EvaluateCastGate"/>.
+/// </summary>
+public enum SpellCastGate
+{
+    /// <summary>Spell metadata is missing / not known.</summary>
+    Unknown,
+    /// <summary>Untargeted, self-targeted, or no target mask — always
+    /// castable. Retail: <c>"CAST %hs"</c> @0x7b63a4.</summary>
+    NoTargetNeeded,
+    /// <summary>A target is selected and compatible. Retail: <c>"CAST
+    /// %hs"</c> @0x7b63a4, then <c>" on %s"</c> @0x7b6464 appended with
+    /// the target's name.</summary>
+    TargetCompatible,
+    /// <summary>A target is selected but incompatible. Retail: <c>"You
+    /// must select an appropriate target for %hs"</c> @0x7b6348.</summary>
+    TargetIncompatible,
+    /// <summary>No target is selected. Retail: <c>"You must select a
+    /// target for %hs"</c> @0x7b63b8.</summary>
+    NoTargetSelected,
+}