refactored internal documentation and simplified comments across chat BLoCs, file viewer, and navigation components

lib/widget/user_avatar.dart

@@ -36,15 +36,12 @@ class _AvatarCacheEntry {
   _AvatarCacheEntry(this.payload, this.fetchedAt);
 }
 
-// Cap keeps the heap bounded for power-users in Talk; TTL ensures
-// server-side avatar updates become visible within a session without
-// requiring an app restart. LinkedHashMap insertion-order plus a remove
-// on hit gives us LRU eviction.
+// LRU via LinkedHashMap insertion order + remove-on-hit. TTL so
+// server-side avatar updates become visible within a session.
 const int _kAvatarCacheMax = 256;
 const Duration _kAvatarCacheTtl = Duration(minutes: 30);
 
-// Resolved payloads are cached so re-mounts render synchronously; in-flight
-// requests are deduped so concurrent mounts share one HTTP call.
+// Pending map dedups concurrent mounts onto a single HTTP call.
 final LinkedHashMap<String, _AvatarCacheEntry> _resolvedAvatars =
     LinkedHashMap<String, _AvatarCacheEntry>();
 final Map<String, Future<_AvatarPayload?>> _pendingAvatars = {};