fix: correct index mapping in electric_power_quality_summaries table (#44)

Fix incorrect index mapping where idx_epqs_summary_interval_start was
indexing the 'id' column instead of the 'summary_interval_start' column.

This issue was introduced when uuid columns were removed and replaced
with id PRIMARY KEY columns. The index name suggests it should index
summary_interval_start, not id.

Changes:
- V3 migration: Change idx_epqs_summary_interval_start to index
  summary_interval_start column instead of id column

Testing:
- All H2 repository tests passing (60+ tests)
- Flyway migrations V1, V2, V3 execute successfully
- Index now correctly targets summary_interval_start column

Fixes issue identified in commit d5e321b where uuid index removal
inadvertently created an incorrectly mapped index.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Sonnet 4.5 <[email protected]>

Author: dfcoffin

openespi-common/src/main/resources/db/migration/V3__Create_additiional_Base_Tables.sql

@@ -641,7 +641,7 @@ CREATE TABLE electric_power_quality_summaries
 );
 
 CREATE INDEX idx_epqs_usage_point_id ON electric_power_quality_summaries (usage_point_id);
-CREATE INDEX idx_epqs_summary_interval_start ON electric_power_quality_summaries (id);
+CREATE INDEX idx_epqs_summary_interval_start ON electric_power_quality_summaries (summary_interval_start);
 CREATE INDEX idx_epqs_created ON electric_power_quality_summaries (created);
 CREATE INDEX idx_epqs_updated ON electric_power_quality_summaries (updated);