feat: Add report bar drilldown drawer (#14626)

## Description

Adds drilldown support for report bar charts powered by
`ReportContainer`. Clicking a non-zero report bar now opens a right-side
drawer with the conversations or messages that contributed to that
bucket, with each row linking to the underlying conversation and message
rows linking with `messageId`.

This includes a new `GET /api/v2/accounts/:account_id/reports/drilldown`
endpoint, backend drilldown builders/serializers, generic chart click
emission, local drawer state via `useReportDrilldown`, compact drilldown
cards, pagination, stale-response protection, and validation for
unsupported drilldown dimensions.

Fixes # CW-4497

https://linear.app/chatwoot/issue/CW-4497/drill-down-on-agent-conversations-report

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality not to work as expected)
- [ ] This change requires a documentation update

## How Has This Been Tested?

Ran the focused backend and frontend checks for the drilldown endpoint,
builder, chart click handling, drawer/card UI, API helper, and
stale-response handling.

Here are the screenshots on how it looks like:
<img width="1792" height="1199" alt="Screenshot 2026-06-02 at 11 32
11 PM"
src="https://github.com/user-attachments/assets/6bdb8832-b9df-4bf3-9a2a-beaefe203b6e"
/>
<img width="1791" height="1230" alt="Screenshot 2026-06-02 at 11 32
34 PM"
src="https://github.com/user-attachments/assets/36e92eb7-3208-4855-87f4-0c7f316df54d"
/>
<img width="1784" height="1235" alt="Screenshot 2026-06-02 at 11 32
46 PM"
src="https://github.com/user-attachments/assets/f7a53916-74f2-4622-9305-042e0ac9e877"
/>



## Checklist:

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

---------

Co-authored-by: Vishnu Narayanan <iamwishnu@gmail.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

app/controllers/api/v2/accounts/reports_controller.rb

@@ -51,6 +51,13 @@ class Api::V2::Accounts::ReportsController < Api::V1::Accounts::BaseController
     generate_csv('conversation_traffic_reports', 'api/v2/accounts/reports/conversation_traffic')
   end
 
+  def drilldown
+    return head :unauthorized unless Current.account_user.administrator?
+    return head :unprocessable_entity unless valid_drilldown_params?
+
+    render json: V2::Reports::DrilldownBuilder.new(Current.account, drilldown_params).build
+  end
+
   def conversations
     return head :unprocessable_entity if params[:type].blank?
 
@@ -133,6 +140,22 @@ class Api::V2::Accounts::ReportsController < Api::V1::Accounts::BaseController
                         })
   end
 
+  def drilldown_params
+    permitted_params = params.permit(
+      :metric, :id, :since, :until, :group_by, :timezone_offset, :bucket_timestamp, :page, :per_page
+    ).to_h.symbolize_keys
+    permitted_params.merge(
+      type: (params[:type].presence || 'account').to_sym,
+      business_hours: ActiveModel::Type::Boolean.new.cast(params[:business_hours])
+    )
+  end
+
+  def valid_drilldown_params?
+    %i[metric bucket_timestamp since until].all? { |param| params[param].present? } &&
+      Reports::ReportMetricRegistry.supported?(params[:metric]) &&
+      V2::Reports::DrilldownBuilder.supported_dimension_type?(params[:type]) && Reports::DrilldownTimestampValidator.valid?(params)
+  end
+
   def conversation_params
     {
       type: params[:type].to_sym,