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/i18n/locale/en/report.json

@@ -121,6 +121,26 @@
       "CLEAR_FILTER": "Clear filter",
       "EMPTY_LIST": "No results found"
     },
+    "DRILLDOWN": {
+      "TITLE": "{metric} details",
+      "RESULT_COUNT_CONVERSATION": "{count} conversation | {count} conversations",
+      "RESULT_COUNT_MESSAGE": "{count} message | {count} messages",
+      "EMPTY": "No records found for this bar.",
+      "ERROR": "Could not load records. Please try again.",
+      "ADMIN_ONLY": "Only administrators can drill down into report records.",
+      "LOAD_MORE": "Load more",
+      "CLOSE": "Close details",
+      "PREVIOUS_BUCKET": "Previous bar",
+      "NEXT_BUCKET": "Next bar",
+      "UNKNOWN_CONTACT": "Unknown contact",
+      "UNKNOWN_INBOX": "Unknown inbox",
+      "UNASSIGNED_AGENT": "Unassigned",
+      "NO_MESSAGE_CONTENT": "No message content",
+      "MESSAGE_CREATED_AT": "Message created at {time}",
+      "EVENT_OCCURRED_AT": "Event occurred at {time}",
+      "INCOMING_MESSAGE": "Incoming message",
+      "OUTGOING_MESSAGE": "Outgoing message"
+    },
     "PAGINATION": {
       "RESULTS": "Showing {start} to {end} of {total} results",
       "PER_PAGE_TEMPLATE": "{size} / page"