Query history panel: no search, no clear-all, no deduplication

## Problem
The query history panel has no search capability and no way to bulk-clear entries. With 35+ history items it becomes unwieldy to navigate.

## Current limitations
1. **No search/filter** — to find a specific past query you must scroll through all entries
2. **No "Clear all" button** — each entry must be deleted individually with the X button
3. **Duplicate entries** — the same query run multiple times accumulates identical entries with no deduplication

## Expected behaviour
- A search/filter input at the top of the history panel to filter by SQL content
- A "Clear all history" button or option
- Optionally: deduplicate identical consecutive queries (keep only the most recent run of each unique SQL)