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/javascript/dashboard/api/reports.js

@@ -31,6 +31,42 @@ class ReportsAPI extends ApiClient {
     });
   }
 
+  getDrilldown({
+    metric,
+    bucketTimestamp,
+    from,
+    to,
+    type = 'account',
+    id,
+    groupBy,
+    businessHours,
+    page,
+    perPage,
+    signal,
+  }) {
+    const requestConfig = {
+      params: {
+        metric,
+        bucket_timestamp: bucketTimestamp,
+        since: from,
+        until: to,
+        type,
+        id,
+        group_by: groupBy,
+        business_hours: businessHours,
+        timezone_offset: getTimeOffset(),
+        page,
+        per_page: perPage,
+      },
+    };
+
+    if (signal) {
+      requestConfig.signal = signal;
+    }
+
+    return axios.get(`${this.url}/drilldown`, requestConfig);
+  }
+
   // eslint-disable-next-line default-param-last
   getSummary(since, until, type = 'account', id, groupBy, businessHours) {
     return axios.get(`${this.url}/summary`, {