docs: Add database query timing documentation and dashboard panel (v0.4.7)

- Add Query Duration Distribution panel to Grafana Runtime dashboard
- Add wordpress_db_query_duration_seconds to Help tab metrics reference
- Add SAVEQUERIES documentation section to README
- Update translation files with new strings

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -292,6 +292,18 @@ add_action( 'wp_prometheus_collect_metrics', function( $collector ) {
 
 ## Session History
 
+### 2026-02-03 - Database Query Timing Documentation (v0.4.7)
+
+- Added database query duration distribution panel to Grafana Runtime dashboard
+- Added `wordpress_db_query_duration_seconds` metric to Help tab metrics reference
+- Added documentation in README explaining how to enable `SAVEQUERIES` for query timing
+- Updated translation files (.pot and .po) with new strings
+- **Key Learning**: WordPress `SAVEQUERIES` constant
+  - Enables `$wpdb->queries` array with query strings, timing, and call stacks
+  - Required for `wordpress_db_query_duration_seconds` histogram metric
+  - Has performance overhead - recommended for development, use cautiously in production
+  - Without it, only query counts are available (not timing data)
+
 ### 2026-02-03 - Dashboard Extension Hook (v0.4.6)
 
 - Added `wp_prometheus_register_dashboards` action hook for third-party plugins