feat: Add inbox-label matrix report endpoint (#13394)

This PR added new API endpoint GET
/api/v2/accounts/:account_id/reports/inbox_label_matrix that returns
conversation counts grouped by inbox and label in a matrix format.
Supports optional filtering by date range, inbox_ids, and label_ids.

---------

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

app/builders/v2/reports/inbox_label_matrix_builder.rb

@@ -0,0 +1,65 @@
+class V2::Reports::InboxLabelMatrixBuilder
+  include DateRangeHelper
+
+  attr_reader :account, :params
+
+  def initialize(account:, params:)
+    @account = account
+    @params = params
+  end
+
+  def build
+    {
+      inboxes: filtered_inboxes.map { |inbox| { id: inbox.id, name: inbox.name } },
+      labels: filtered_labels.map { |label| { id: label.id, title: label.title } },
+      matrix: build_matrix
+    }
+  end
+
+  private
+
+  def filtered_inboxes
+    @filtered_inboxes ||= begin
+      inboxes = account.inboxes
+      inboxes = inboxes.where(id: params[:inbox_ids]) if params[:inbox_ids].present?
+      inboxes.order(:name).to_a
+    end
+  end
+
+  def filtered_labels
+    @filtered_labels ||= begin
+      labels = account.labels
+      labels = labels.where(id: params[:label_ids]) if params[:label_ids].present?
+      labels.order(:title).to_a
+    end
+  end
+
+  def conversation_filter
+    filter = { account_id: account.id }
+    filter[:created_at] = range if range.present?
+    filter[:inbox_id] = params[:inbox_ids] if params[:inbox_ids].present?
+    filter
+  end
+
+  def fetch_grouped_counts
+    label_names = filtered_labels.map(&:title)
+    return {} if label_names.empty?
+
+    ActsAsTaggableOn::Tagging
+      .joins('INNER JOIN conversations ON taggings.taggable_id = conversations.id')
+      .joins('INNER JOIN tags ON taggings.tag_id = tags.id')
+      .where(taggable_type: 'Conversation', context: 'labels', conversations: conversation_filter)
+      .where(tags: { name: label_names })
+      .group('conversations.inbox_id', 'tags.name')
+      .count
+  end
+
+  def build_matrix
+    counts = fetch_grouped_counts
+    filtered_inboxes.map do |inbox|
+      filtered_labels.map do |label|
+        counts[[inbox.id, label.title]] || 0
+      end
+    end
+  end
+end