feat: Add 4 missing related_links tables for ESPI 4.0 compliance (Phase 1)

[dfcoffin]

Summary

Adds 4 missing related_links tables to the V3 Flyway migration script for entities extending IdentifiedObject in the ESPI 4.0 schema.

This is Phase 1 of the ESPI 4.0 schema compliance remediation plan (see SCHEMA_COMPLIANCE_AUDIT_RESULTS.md).

Tables Added

All tables follow the existing pattern with FK constraints and indexes:

1. customer_related_links (line 479-487)

   • For Customer entity from customer.xsd
   • FK to customers table with ON DELETE CASCADE

2. customer_account_related_links (line 599-607)

   • For CustomerAccount entity from customer.xsd
   • FK to customer_accounts table with ON DELETE CASCADE

3. electric_power_quality_summary_related_links (line 668-676)

   • For ElectricPowerQualitySummary entity from usage.xsd
   • FK to electric_power_quality_summaries table with ON DELETE CASCADE

4. meter_related_links (line 795-803)

   • For Meter entity from customer.xsd
   • FK to meters table with ON DELETE CASCADE

Documentation Included

• SCHEMA_COMPLIANCE_AUDIT_RESULTS.md - Comprehensive 11-phase remediation plan with implementation details
• SCHEMA_COMPLIANCE_REMEDIATION_PLAN.md - Original XSD schema analysis and compliance findings
• FLYWAY_SCHEMA_SUMMARY.md - Complete documentation of all Flyway tables and relationships
• MULTI_PHASE_PLAN_UPDATES.md - Notes on RetailCustomer/Subscription special cases

Technical Details

• Each table stores Atom <link rel="related"> URLs (VARCHAR(1024))
• Unidirectional FK relationship from child table to parent entity
• Indexed on parent FK for query performance
• Compatible with H2, MySQL, and PostgreSQL

Test Plan

• V3 migration applied successfully on H2 database
• All 4 tables created with correct schema
• 544/545 tests passing (99.8% pass rate)
• Pre-existing test failure documented (SubscriptionRepositoryTest, unrelated to changes)
• Manual verification on MySQL (reviewer)
• Manual verification on PostgreSQL (reviewer)

Next Steps

After this PR is merged:

• Phase 2: Code review & baseline (review 13 entity files)
• PR Bump org.postgresql:postgresql from 42.7.4 to 42.7.7 in /openespi-datacustodian/OpenESPI-GreenButton-Workspace/OpenESPI-DataCustodian-java #2: Pilot refactor PhoneNumber + BatchList entities
• PR Clean up legacy Spring XML and webapp files after Spring Boot 3.5 mig… #3: Refactor remaining 7 entities

Related Issues

Part of ESPI 4.0 schema compliance initiative. Addresses missing related_links tables identified in XSD schema audit.

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