perf: skip conversation loading in /meta endpoint (#13564)

# Pull Request Template

## Summary
- Adds `perform_meta_only` method to `ConversationFinder` that runs
setup and counts without loading the paginated conversation list
- Updates `/api/v1/conversations/meta` to use `perform_meta_only`
instead of `perform`

## Problem
The `/meta` endpoint calls `ConversationFinder#perform` which:
1. Runs all filters and setup (`set_up`)
2. Computes 3 COUNT queries (`set_count_for_all_conversations`)
3. Filters by assignee type
4. **Builds the full paginated conversation list** with
`.includes(:taggings, :inbox, {assignee: {avatar_attachment: [:blob]}},
{contact: {avatar_attachment: [:blob]}}, :team, :contact_inbox)` +
sorting + pagination

The controller then **discards the conversations** and only uses the
counts:
```ruby
def meta
result = conversation_finder.perform
@conversations_count = result[:count]  # conversations thrown away
end
```

## Type of change

- [x] Performance fix

## How Has This Been Tested?

- [ ] Verify /meta returns correct mine/unassigned/assigned/all counts
- [ ] Verify counts update when switching inbox, team, or status filters
- [ ] Verify conversation list still loads correctly (uses perform, not
affected)
- [ ] Monitor response time reduction for /meta in NewRelic after deploy

## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

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

app/controllers/api/v1/accounts/conversations_controller.rb

@@ -15,7 +15,7 @@ class Api::V1::Accounts::ConversationsController < Api::V1::Accounts::BaseContro
   end
 
   def meta
-    result = conversation_finder.perform
+    result = conversation_finder.perform_meta_only
     @conversations_count = result[:count]
   end
 

app/finders/conversation_finder.rb

@@ -55,6 +55,22 @@ class ConversationFinder
     }
   end
 
+  def perform_meta_only
+    set_up
+
+    mine_count, unassigned_count, all_count, = set_count_for_all_conversations
+    assigned_count = all_count - unassigned_count
+
+    {
+      count: {
+        mine_count: mine_count,
+        assigned_count: assigned_count,
+        unassigned_count: unassigned_count,
+        all_count: all_count
+      }
+    }
+  end
+
   private
 
   def set_up

spec/finders/conversation_finder_spec.rb

@@ -190,6 +190,32 @@ describe ConversationFinder do
       end
     end
 
+    context 'with perform_meta_only' do
+      let(:params) { { assignee_type: 'assigned' } }
+
+      it 'returns only count without conversations' do
+        result = conversation_finder.perform_meta_only
+        expect(result).to have_key(:count)
+        expect(result).not_to have_key(:conversations)
+      end
+
+      it 'returns the correct counts' do
+        result = conversation_finder.perform_meta_only
+        expect(result[:count]).to eq({
+                                       mine_count: 2,
+                                       assigned_count: 3,
+                                       unassigned_count: 1,
+                                       all_count: 4
+                                     })
+      end
+
+      it 'returns same counts as perform' do
+        meta_result = conversation_finder.perform_meta_only
+        full_result = conversation_finder.perform
+        expect(meta_result[:count]).to eq(full_result[:count])
+      end
+    end
+
     context 'with unattended' do
       let(:params) { { status: 'open', assignee_type: 'me', conversation_type: 'unattended' } }