feat(ui): FA3 -- mount the social panel shell (Friends/Allegiance/Fellowship/Squelch)

Campaign FA slice FA3: retail's four-tab social panel (LayoutDesc
0x2100006E slot 0x1000018F, RetailPanelCatalog id 12), built on the OP3
OptionsPanelController recipe -- Type-8 tab host, ActivateTabBehavior,
per-page scoped controllers.

- SocialPanelController mounts the tab host and wires the close button;
  F3 (ToggleAllegiancePanel) and F4 (ToggleFellowshipPanel) open the
  panel and switch to their own tab, sharing the same gmPanelUI
  one-active-panel exclusivity every sibling main panel already has.
- The live-DAT tab table CORRECTS the coordinator addendum's x-order
  guess: button 0x1000028C ("Allegiance") pairs with page 0x10000291 and
  is the authored DEFAULT entry, not Friends -- each button's own page
  id and its own P0x57 (matching the F3/F4 ActionMap ids on the
  Allegiance/Fellowship pages specifically) both corroborate the real
  pairing. See SocialPanelController's class doc for the full table.
- SocialFellowshipPageController swaps the two authored empty/full
  frames (0x1000026B/0x10000275) on RuntimeFellowshipState's
  IsInFellowship -- both frames' full containment (name box, create
  button, checkboxes vs. roster list, six buttons) was confirmed by the
  live-mount probe, so a single Visible toggle per frame is the whole
  swap (closes lane-A unknown U6).
- SocialAllegiancePageController hides the monarch/patron blocks and
  blanks their name text to a literal space when
  RuntimeAllegianceState.Snapshot.HasProfile is false, using SCOPED
  FindDescendant lookups (the panel authors 0x10000492 twice, once per
  block).
- SocialFriendsPageController/SocialSquelchPageController bind their
  ListBoxes read-only to RuntimeCommunicationState's existing J4.1
  Friends/Squelch owners (names only), rebuilding on revision change.
  Their action buttons are honest INERT (D1) -- register row AD-79.
- UiTemplateListBox gains Flush() (lane A/D's "Gap found" prerequisite)
  so a poll-and-rebuild list can shrink between refreshes.
- RetailPanelCatalog.SocialPanel = 12, byte-verified from the live slot's
  own P0x10000029; listed in Mounted only (no toolbar button -- lane A
  §6.1: the open path is keyboard-only).

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

src/AcDream.App/UI/Layout/SocialFriendsPageController.cs

@@ -0,0 +1,94 @@
+using System;
+using System.Numerics;
+using AcDream.Core.Social;
+
+namespace AcDream.App.UI.Layout;
+
+/// <summary>
+/// Campaign FA slice FA3, D1: the Friends page's read-only roster — names
+/// only, bound directly to the J4.1 <see cref="FriendsState"/> owner
+/// (<c>RuntimeCommunicationState.Friends</c>). Rebuilds on
+/// <see cref="FriendsState.Revision"/> change; polled every frame from
+/// <see cref="SocialPanelController.Tick"/> (cheap — a single
+/// <see langword="long"/> comparison when nothing changed).
+///
+/// <para>
+/// <b>D1 — inert actions.</b> This campaign implements no Friends
+/// add/remove/appear-offline wire (the trivially-pinnable bar D1 sets was
+/// not met for this family — see the plan's D1 decision). The three
+/// buttons (<c>0x10000514</c>/<c>0x10000515</c>/<c>0x10000516</c>) and the
+/// "Appear Offline" checkbox (<c>0x1000052C</c>) are left AUTHORED and
+/// CLICKABLE with no handler — <see cref="DatWidgetFactory"/> already
+/// builds every button/checkbox with a null <c>OnClick</c> by default, so
+/// no explicit "leave unbound" code is needed here. See this commit's
+/// single register row covering the whole D1 Friends/Squelch inert-actions
+/// scope (one row, not one per button).
+/// </para>
+///
+/// <para>
+/// Row template <c>0x2100005D</c>/<c>0x10000519</c> (FA3 live-mount probe);
+/// <see cref="SocialPanelRowText.FindDeepest"/> resolves the row's own
+/// name-text leaf — see that class's doc for why the deepest match is used
+/// (gmFriendsUI is outside this campaign's decompiled scope).
+/// </para>
+/// </summary>
+public sealed class SocialFriendsPageController
+{
+    private const uint ListBoxId = 0x10000517u;
+
+    private readonly UiTemplateListBox _listBox;
+    private readonly FriendsState _friends;
+    private long _lastRevision = long.MinValue;
+
+    private SocialFriendsPageController(UiTemplateListBox listBox, FriendsState friends)
+    {
+        _listBox = listBox;
+        _friends = friends;
+    }
+
+    public static SocialFriendsPageController? Bind(
+        UiElement pageRoot,
+        FriendsState friends,
+        Func<uint, uint, UiElement?> templateResolver)
+    {
+        ArgumentNullException.ThrowIfNull(pageRoot);
+        ArgumentNullException.ThrowIfNull(friends);
+        ArgumentNullException.ThrowIfNull(templateResolver);
+
+        if (UiElement.FindDescendant(pageRoot, ListBoxId) is not UiTemplateListBox listBox)
+        {
+            Console.WriteLine(
+                $"[D.2b] SocialFriendsPageController: ListBox 0x{ListBoxId:X8} not "
+                + "found — Friends page will not populate.");
+            return null;
+        }
+        listBox.TemplateResolver = templateResolver;
+
+        var controller = new SocialFriendsPageController(listBox, friends);
+        controller.Refresh();
+        return controller;
+    }
+
+    public void Tick()
+    {
+        long revision = _friends.Revision;
+        if (revision == _lastRevision) return;
+        Refresh();
+    }
+
+    private void Refresh()
+    {
+        _lastRevision = _friends.Revision;
+        _listBox.Flush();
+        foreach (FriendEntry friend in _friends.Snapshot())
+        {
+            UiElement? row = _listBox.AddItemFromTemplateList(0);
+            if (row is null) continue;
+            if (SocialPanelRowText.FindDeepest(row) is { } text)
+            {
+                string name = friend.Name;
+                text.LinesProvider = () => [new UiText.Line(name, Vector4.One)];
+            }
+        }
+    }
+}