Fix two Copilot review nits

1) ActivityUnversionedFallback XML doc previously claimed MatchStrategy
   does not gate activity dispatch. That's incorrect: GrpcDurableTaskWorker's
   OnRunActivityAsync calls EvaluateOrchestrationVersioning against the
   activity work item's version (set via TaskOptions.Version at schedule
   time, or inherited from the calling orchestration when null), and the
   strict-mode work-item filter narrows activity filters too. Rewrote the
   interaction bullet to match actual behavior.

2) UnversionedFallbackSample/Program.cs had a comment saying orchestrator
   fallback was 'commented below' while the next line actively enabled it.
   Rewrote the comment to match what the sample actually does: both flags
   are enabled to demonstrate orchestrator catch-all dispatch; the advice
   to start with activity-only stays as guidance for the reader's own code.

Addresses Copilot review feedback at #discussion_r3305294155 and #discussion_r3305294212.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: torosent

samples/UnversionedFallbackSample/Program.cs

@@ -27,9 +27,10 @@
     wb.AddTasks(tasks => tasks.AddAllGeneratedTasks());
     wb.UseVersioning(new DurableTaskWorkerOptions.VersioningOptions
     {
-        // Activity fallback is the safer place to start: activities are stateless and do not replay
-        // history. Enable orchestrator fallback (commented below) only when the unversioned
-        // orchestrator is replay-compatible with every version it may receive.
+        // This sample enables CatchAll fallback on both sides. Activity fallback is the safer place to
+        // start in your own code (activities are stateless and don't replay history); only enable
+        // orchestrator fallback when the unversioned orchestrator is replay-compatible with every
+        // version it may receive.
         ActivityUnversionedFallback = DurableTaskWorkerOptions.UnversionedFallbackMode.CatchAll,
         OrchestratorUnversionedFallback = DurableTaskWorkerOptions.UnversionedFallbackMode.CatchAll,
     });

src/Worker/Core/DurableTaskWorkerOptions.cs

@@ -364,8 +364,12 @@ public class VersioningOptions
         /// <list type="bullet">
         ///   <item><description>Unlike <see cref="FailureStrategy"/>, this setting applies regardless of
         ///   <see cref="MatchStrategy"/>.</description></item>
-        ///   <item><description><see cref="MatchStrategy"/> applies to orchestration instance versions, not
-        ///   activity scheduling versions, so it does not gate activity dispatch.</description></item>
+        ///   <item><description>When <see cref="MatchStrategy"/> is not <see cref="VersionMatchStrategy.None"/>,
+        ///   the pre-dispatch versioning gate also evaluates the activity work item's version (set via
+        ///   <c>TaskOptions.Version</c> at schedule time, or inherited from the calling orchestration's
+        ///   instance version when <c>TaskOptions.Version</c> is <c>null</c>) and rejects mismatches per
+        ///   <see cref="FailureStrategy"/>. This setting governs only how the factory resolves activity
+        ///   work items that pass the gate.</description></item>
         /// </list>
         /// </remarks>
         public UnversionedFallbackMode ActivityUnversionedFallback { get; set; } = UnversionedFallbackMode.Implicit;