Allow operators to delete their own query history

## Problem

The dashboard now stores server-side message and trace query history, shows both lists in the Message Explorer history drawer, and automatically purges records only after the configured retention period. The drawer does not provide a way for an operator to remove an individual history entry or clear their own history on demand.

This matters in shared environments where a query can contain a sensitive message key, topic, message ID, or trace topic. Waiting for scheduled retention, or changing the global retention setting, is not an adequate way for an operator to remove an entry immediately. The current UI also makes the history appear permanent even though it is user-scoped.

## Expected behavior

- allow an authenticated operator to delete one of their own message-query or trace-query history records;
- provide a clear-history action for the current operator and selected cluster scope;
- never allow a user to delete another operator's records;
- refresh the list and summary after deletion, including when the last row on a page is removed;
- require confirmation before clearing multiple records.

The existing scheduled retention cleanup should remain as the automatic backstop.

## Scope

This issue is about the server-side query history API and the Message Explorer history drawer. Saved query presets are a separate feature and are not part of this issue.

Start with the server-side query history API and the Message Explorer history drawer, then trace the existing scheduled retention cleanup to understand the stored records and cluster scope. Done means operators can delete their own message or trace history entries, confirm clearing multiple records, and see the list and summary refresh correctly without affecting another operator's records.

Written by the indexing model from the issue text.