Add clarifying comments for accessibility implementation

- Explain why accessibility delegate is not set during batch selection
- Explain why map is cleared and rebuilt on each accessibility update
- Improves code maintainability and readability

Co-authored-by: adbenitez <24558636+adbenitez@users.noreply.github.com>

src/main/java/org/thoughtcrime/securesms/ConversationItem.java

@@ -431,7 +431,10 @@ public class ConversationItem extends BaseConversationItem
       bodyText.setText(spannable);
       bodyText.setVisibility(View.VISIBLE);
       
-      // Set accessibility delegate for TalkBack to expose links as custom actions
+      // Set accessibility delegate for TalkBack to expose links as custom actions.
+      // Note: During batch selection mode (batchSelected.isEmpty() == false), links are not
+      // linkified (see line 427-428), so there's no need to set the accessibility delegate.
+      // This also ensures that accessibility focus doesn't interfere with batch selection UI.
       if (Util.isTouchExplorationEnabled(context) && batchSelected.isEmpty()) {
         if (linkAccessibilityDelegate == null) {
           linkAccessibilityDelegate = new LinkAccessibilityDelegate(context);

src/main/java/org/thoughtcrime/securesms/util/LinkAccessibilityDelegate.java

@@ -53,7 +53,10 @@ public class LinkAccessibilityDelegate extends View.AccessibilityDelegate {
     Spanned spanned = (Spanned) text;
     LongClickCopySpan[] spans = spanned.getSpans(0, spanned.length(), LongClickCopySpan.class);
     
-    // Clear previous mappings
+    // Clear and rebuild mappings each time. This is necessary because:
+    // 1. TextView content may have changed since the last call
+    // 2. The same delegate instance may be reused for different text content
+    // 3. This method is called infrequently enough that performance is not a concern
     actionSpanMap.clear();
     
     // Add a custom action for each link