Highlight selected grid row on performance trend charts #683

Summary

When a user selects a row in a query/procedure grid, the performance trend chart above doesn't react. The user has to double-click, open a modal history window, and mentally correlate timing.

Proposed Behavior

When a row is selected in a query grid (Top Queries, Top Procedures, Query Store), overlay that specific query's trend line on the existing performance trend chart — or highlight its data points. This instantly answers "is this query always expensive or did it just get bad recently?"

This is lightweight — no popup or navigation required. Just a visual reaction: click row → chart responds.

Example Flow

1. User is on the Query Performance tab, looking at the duration trend chart and the Top Queries grid
2. User clicks a row for a query with high avg duration
3. The duration trend chart overlays that query's individual duration trend as a highlighted line
4. User can immediately see whether the query recently regressed or has always been slow

Design Notes

• The overlay should be visually distinct (brighter color, thicker line) from the aggregate trend
• Deselecting the row (or selecting a different row) should clear/replace the overlay
• Data for the individual query trend is already available via GetQueryTrendAsync by query_hash
• Applies to both Dashboard and Lite

Complexity: Low — visual overlay on existing charts, data fetch method already exists.