perf(messages): restructure format-string call sites (#2437)

## Summary

Phase 3 PR B of the message-interpolation cleanup. Handles the multi-line restructure sites flagged in `dev-docs/string-handling-message-interp-audit.md` (Phase 2). Phase 3.1 (PR #2436) handled trivial sweeps; this PR handles sites that needed an `if/else` hoist or switch restructure to eliminate `string.Format` while preserving exact message text.

Each site previously allocated an intermediate `string.Format(...)` result before passing to the message handler, despite Phase 1 making the handler accept interpolated string handlers natively.

## Sites fixed

- **`Projects/Server/Mobiles/Mobile.cs:7911`** - Title/guild header was using `string.Format` with a conditional template (`"[{1}]{2}"` vs `"[{0}, {1}]{2}"`). Split into `if (title.Length <= 0)` / `else` with direct `$"..."` interpolation.
- **`Projects/UOContent/Engines/ConPVP/DuelContext.cs:1337`** - View-ladder rank text used `string.Format(text, from == pm ? "You" : "They")`. Split into `if (from == pm)` / `else` with direct `$"..."` interpolation in each branch.
- **`Projects/UOContent/Engines/ConPVP/DuelContext.cs:1463`** - Showladder text reused a single format string for both `LocalOverheadMessage` ("You ... are ...") and `NonlocalOverheadMessage` ("`{pm.Name}` ... is ..."). Each call now uses an inline `$"..."` directly; no shared template.
- **`Projects/UOContent/Engines/ConPVP/Gumps/ConfirmSignupGump.cs:518`** - The signup confirmation message used a `switch` expression assigning a literal format string to `fmt`, then `string.Format(fmt, from.Female ? "Lady" : "Lord", timeUntil)`. Converted to a `switch` statement where each case calls `_registrar.PrivateOverheadMessage(...)` directly with an inline `$"..."`. Lady/Lord branching is hoisted to a `title` local.

## Exempted

- **`Projects/UOContent/Engines/ConPVP/Participant.cs:138`** - The `nonLocalOverhead` format string is a parameter passed in by callers of `Participant.Broadcast`. Investigation found 5 call sites in `DuelContext.cs` (lines 782, 802, 1187, 1196, and three at 1535/1564/1608) that pass distinct literal format strings. Refactoring would require changing all 5 callers and the method signature - out of scope for this PR. Marked with a `// Phase 3 audit:` comment per the audit's exemption convention.

Projects/UOContent/Engines/ConPVP/DuelContext.cs

@@ -1334,16 +1334,26 @@ public partial class DuelContext
                 return; // sanity
             }
 
-            var text =
-                $"{{0}} are ranked {LadderGump.Rank(entry.Index + 1)} at level {Ladder.GetLevel(entry.Experience)}.";
-
-            pm.PrivateOverheadMessage(
-                MessageType.Regular,
-                pm.SpeechHue,
-                true,
-                string.Format(text, from == pm ? "You" : "They"),
-                from.NetState
-            );
+            if (from == pm)
+            {
+                pm.PrivateOverheadMessage(
+                    MessageType.Regular,
+                    pm.SpeechHue,
+                    true,
+                    $"You are ranked {LadderGump.Rank(entry.Index + 1)} at level {Ladder.GetLevel(entry.Experience)}.",
+                    from.NetState
+                );
+            }
+            else
+            {
+                pm.PrivateOverheadMessage(
+                    MessageType.Regular,
+                    pm.SpeechHue,
+                    true,
+                    $"They are ranked {LadderGump.Rank(entry.Index + 1)} at level {Ladder.GetLevel(entry.Experience)}.",
+                    from.NetState
+                );
+            }
         }
         else if (obj is Mobile mob)
         {
@@ -1460,15 +1470,17 @@ public partial class DuelContext
                         return; // sanity
                     }
 
-                    var text =
-                        $"{{0}} {{1}} ranked {LadderGump.Rank(entry.Index + 1)} at level {Ladder.GetLevel(entry.Experience)}.";
-
-                    pm.LocalOverheadMessage(MessageType.Regular, pm.SpeechHue, true, string.Format(text, "You", "are"));
+                    pm.LocalOverheadMessage(
+                        MessageType.Regular,
+                        pm.SpeechHue,
+                        true,
+                        $"You are ranked {LadderGump.Rank(entry.Index + 1)} at level {Ladder.GetLevel(entry.Experience)}."
+                    );
                     pm.NonlocalOverheadMessage(
                         MessageType.Regular,
                         pm.SpeechHue,
                         true,
-                        string.Format(text, pm.Name, "is")
+                        $"{pm.Name} is ranked {LadderGump.Rank(entry.Index + 1)} at level {Ladder.GetLevel(entry.Experience)}."
                     );
 
                     // pm.PublicOverheadMessage( MessageType.Regular, pm.SpeechHue, true, String.Format( "Level {0} with {1} win{2} and {3} loss{4}.", Ladder.GetLevel( entry.Experience ), entry.Wins, entry.Wins==1?"":"s", entry.Losses, entry.Losses==1?"":"es" ) );