feat(chat): CT-A5 — clicking a speaker's name opens a tell

Campaign CT slice A5, closing Group A. Retail's
gmMainChatUI::RecvNotice_TextTag_IIDStringClick @0x004CCE10 ->
ChatInterface::StartTell @0x004F41F0 writes "@tell {Name}, " into the chat
entry and takes keyboard focus; clicking a green name here now does the same.

The trailing space is deliberate — without it the first character the player
types joins the comma.

Three seams, each narrow on purpose:

  - UiText.OnCharClick is offered the character under a left click before the
    element-wide OnClick, and consuming it suppresses that. Kept separate
    because a tag click is POSITIONAL and an element click is not; folding
    them together would make every text element with an OnClick swallow tag
    clicks.
  - TaggedRangesForFragment returns tagged column ranges relative to the
    FRAGMENT, because that is what a click resolves to — UiText.HitChar gives
    a line index into the WRAPPED list plus a column within it. Line-relative
    ranges would land every click on a wrapped line at the wrong characters.
  - The controller caches those ranges alongside the runs it already caches,
    so the per-click lookup reads the same cache the draw does.

The hit test is half-open: a caret slot sits BETWEEN glyphs, so clicking just
past a name's last letter belongs to the space after it, not the name. Pinned
by theory rather than left to chance, since off-by-one here means clicking a
name sometimes does nothing.

StartTell uses the tag's NAME, not its object id — retail carries the id but
this handler never reads it, so the tell still addresses correctly for someone
who has since moved out of range.

Group A is complete: names are green (A4) and clickable (A5). Ready for the
user's visual gate.

Solution builds clean; full hermetic gate green.

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

tests/AcDream.App.Tests/UI/Layout/ChatWindowControllerTests.cs

@@ -158,6 +158,25 @@ public class ChatWindowControllerTests
         Assert.NotNull(ctrl);
     }
 
+    [Fact]
+    public void StartTell_PrefillsTheEntryAndPutsTheCaretAtTheEnd()
+    {
+        // Retail's ChatInterface::StartTell @0x004F41F0 writes "@tell {Name}, "
+        // into the chat entry and takes focus, so the player can type straight
+        // into a reply. The trailing space matters: without it the first thing
+        // they type joins the comma.
+        var (rootInfo, layout, vm) = BuildTestTree();
+        var bus = new CaptureBus();
+
+        ChatWindowController? ctrl = ChatWindowController.Bind(
+            rootInfo, layout, vm, () => bus, new ChatWindowState(), null, null, NoTex);
+        Assert.NotNull(ctrl);
+
+        ctrl!.StartTell("Dww");
+
+        Assert.Equal("@tell Dww, ", ctrl.Input.Text);
+    }
+
     // ── Talk-focus specials: "Tell to X" / "Squelch (ignore) X" ─────────────
 
     /// <summary>