feat(runtime): FA4 -- fellowship roster enumeration + Social selection source

IRuntimeFellowshipView.GetMembers() gives the fellowship panel a way to
enumerate the whole roster (TryGetMember alone needs the guid first,
which a UI roster build doesn't have yet). Implemented on
RuntimeFellowshipState.FellowshipView as a materialized snapshot under
the same lock every other read there uses.

SelectionChangeSource.Social covers a fellowship-roster row click
(gmFellowshipUI's list-selection arm calls the same
ACCWeenieObject::SetSelectedObject primitive every other selection
origin uses -- lane B docs/research/2026-08-11-fa-panel-structure.md
§6.2/§2.8).

Runtime tests: +4 (RuntimeFellowshipStateTests.GetMembers_*).

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

src/AcDream.Runtime/GameRuntimeGameplayViews.cs

@@ -154,6 +154,18 @@ public interface IRuntimeFellowshipView
     RuntimeFellowshipSnapshot Snapshot { get; }
 
     bool TryGetMember(uint guid, out RuntimeFellowMemberSnapshot member);
+
+    /// <summary>
+    /// Campaign FA slice FA4: the complete member roster, for the
+    /// fellowship page's row-per-fellow list. <see cref="TryGetMember"/>
+    /// alone cannot build a roster — it needs the guid first. Order is
+    /// insertion order (the last <c>0x02BE FellowshipFullUpdate</c>'s
+    /// wire order, then whatever order incremental <c>0x02C0</c> upserts
+    /// added new members) — retail's own hash-table iteration order is not
+    /// a stable contract either (lane B §3.9), so no ordering guarantee
+    /// beyond "stable across repeated calls between mutations" is made.
+    /// </summary>
+    IEnumerable<RuntimeFellowMemberSnapshot> GetMembers();
 }
 
 public readonly record struct RuntimeAllegianceMemberSnapshot(