perf: Migrate Old Guild System gumps to DynamicGump (#2420)

## Summary

Migrates the Old Guild System (pre-AOS guild stones) gumps from the legacy `Gump` class to `DynamicGump`, following the same pattern used for the Quest gump migration in #2416. All concrete gumps now have private constructors gated by static `DisplayTo` entry points (empty-gump rule), and `Singleton => true` is set across the board so reopening a sibling dialog automatically closes the previous one.

**Migrated gumps:**
- `GuildGump` - main guild dialog
- `GuildmasterGump` - guildmaster functions
- `GuildCharterGump` - charter and website display
- `GuildWarGump` - warfare status (kept as player-facing)
- `GuildWarAdminGump` - war menu (retained as player-facing - reachable from `GuildmasterGump`'s WAR button by guildmasters)
- `GuildChangeTypeGump` - Standard/Order/Chaos selection

**Abstract bases:** `GuildListGump` and `GuildMobileListGump` keep their shared list-rendering chrome inside a single concrete `BuildLayout` on the abstract class and expose a `protected abstract void BuildHeader(ref DynamicGumpBuilder builder)` hook for subclasses (replacing the old `Design()` override). This mirrors the abstract-base treatment used for the ML quest base in the quest-gump migration PR.

**Concrete subclasses migrated alongside the abstract bases:**
- `GuildListGump` subclasses: `GuildAcceptWarGump`, `GuildDeclarePeaceGump`, `GuildDeclareWarGump`, `GuildRejectWarGump`, `GuildRescindDeclarationGump`
- `GuildMobileListGump` subclasses: `DeclareFealtyGump`, `GrantGuildTitleGump`, `GuildAdminCandidatesGump`, `GuildCandidatesGump`, `GuildDismissGump`, `GuildRosterGump`

**Cliloc rule:** Every gump bakes per-instance dynamic content (guild names, member names, war declarations, candidate lists), which would defeat `StaticGump<T>` caching. Per the cliloc rule, all are `DynamicGump`.

**External callers updated:** the prompt files (`GuildAbbrvPrompt`, `GuildCharterPrompt`, `GuildDeclareWarPrompt`, `GuildNamePrompt`, `GuildTitlePrompt`, `GuildWebsitePrompt`), `RecruitTarget`, the `Guildstone` item, and the New Guild System `GuildInfoGump`'s Order/Chaos handler all now go through static `DisplayTo` entry points instead of `new XGump(...)`.

Projects/UOContent/Gumps/Guilds/GuildNamePrompt.cs

@@ -1,3 +1,4 @@
+using System;
 using Server.Guilds;
 using Server.Prompts;
 
@@ -5,55 +6,49 @@ namespace Server.Gumps
 {
     public class GuildNamePrompt : Prompt
     {
-        private readonly Guild m_Guild;
-        private readonly Mobile m_Mobile;
+        private readonly Guild _guild;
 
-        public GuildNamePrompt(Mobile m, Guild g)
-        {
-            m_Mobile = m;
-            m_Guild = g;
-        }
+        public GuildNamePrompt(Mobile m, Guild g) => _guild = g;
 
         public override void OnCancel(Mobile from)
         {
-            if (GuildGump.BadLeader(m_Mobile, m_Guild))
+            if (GuildGump.BadLeader(from, _guild))
             {
                 return;
             }
 
-            GuildGump.EnsureClosed(m_Mobile);
-            m_Mobile.SendGump(new GuildmasterGump(m_Mobile, m_Guild));
+            GuildmasterGump.DisplayTo(from, _guild);
         }
 
         public override void OnResponse(Mobile from, string text)
         {
-            if (GuildGump.BadLeader(m_Mobile, m_Guild))
+            if (GuildGump.BadLeader(from, _guild))
             {
                 return;
             }
 
-            text = text.Trim();
+            var textSpan = text.AsSpan().Trim();
 
-            if (text.Length > 40)
+            if (textSpan.Length > 40)
             {
-                text = text[..40];
+                textSpan = textSpan[..40];
             }
 
-            if (text.Length > 0)
+            if (textSpan.Length > 0)
             {
-                if (BaseGuild.FindByName(text) != null)
+                if (BaseGuild.FindByName(textSpan) != null)
                 {
-                    m_Mobile.SendMessage($"{text} conflicts with the name of an existing guild.");
+                    from.SendMessage($"{textSpan} conflicts with the name of an existing guild.");
                 }
                 else
                 {
-                    m_Guild.Name = text;
-                    m_Guild.GuildMessage(1018024, true, text); // The name of your guild has changed:
+                    text = textSpan.ToString();
+                    _guild.Name = text;
+                    _guild.GuildMessage(1018024, true, text); // The name of your guild has changed:
                 }
             }
 
-            GuildGump.EnsureClosed(m_Mobile);
-            m_Mobile.SendGump(new GuildmasterGump(m_Mobile, m_Guild));
+            GuildmasterGump.DisplayTo(from, _guild);
         }
     }
 }