Add Producer Group client composition report

### Problem

Producer Connection currently summarizes an entire topic query. When several Producer Groups are returned together, operators cannot identify which group contains duplicate client IDs, mixed client versions/languages, or incomplete client metadata without manually separating rows.

### Proposed change

Add a read-only composition report based on the current query result that:

- groups connections by reported Producer Group;
- reports connection, unique client, and unique address counts;
- displays language and version distributions per group;
- flags duplicate client IDs within a group, version/language diversity, incomplete metadata, and unreported groups;
- supports filtering, expandable client/address evidence, CSV export, bilingual copy, and focused tests.

The report should make version diversity visible without claiming that different versions are inherently incompatible, and it should not issue additional backend requests.

Start by locating the Producer Connection view and the current topic-query result handling, then find the focused tests for that view. Verify how group, client, address, language, version, and metadata fields are currently represented before scoping the report. Done means the report uses only the existing result, exposes the requested evidence, filters and CSV export, includes bilingual copy, and has focused tests.

Written by the indexing model from the issue text.