chore(refactor): Improve conversation permission filtering (#11166)

1. Add permission filter service to separate permission filtering logic
from conversation queries
2. Implement hierarchical permissions with cleaner logic:
   - conversation_manage gives access to all conversations
- conversation_unassigned_manage gives access to unassigned and user's
conversations
- conversation_participating_manage gives access only to user's
conversations

---------

Co-authored-by: Pranav <pranav@chatwoot.com>

app/finders/conversation_finder.rb

@@ -93,6 +93,12 @@ class ConversationFinder
 
   def find_all_conversations
     find_conversation_by_inbox
+    # Apply permission-based filtering
+    @conversations = Conversations::PermissionFilterService.new(
+      @conversations,
+      current_user,
+      current_account
+    ).perform
     filter_by_conversation_type if params[:conversation_type]
     @conversations
   end