Add post-migration validation scripts for Cosmos DB to SQL migration

[Copilot]

Description

Post-migration validation suite: SQL scripts + PowerShell runner to verify data integrity, row counts, and performance after Cosmos DB → SQL migration.

Type of Change

• New feature (non-breaking change which adds functionality)
• Documentation update

Changes Made

• Scripts/PostMigration/01-RowCountValidation.sql — Compares expected vs actual row counts per table with configurable tolerance, PASS/FAIL/WARNING per table
• Scripts/PostMigration/02-DataIntegrityChecks.sql — FK orphan detection, index/PK existence, CHECKSUM_AGG per table, NOT NULL compliance
• Scripts/PostMigration/03-SampleDataComparison.sql — First/last N rows per table (PK-ordered), column type summary, empty table warnings
• Scripts/PostMigration/04-PerformanceBaseline.sql — Space usage, index usage stats, fragmentation, scan timing, wait stats, missing index suggestions
• Scripts/PostMigration/RunAllValidations.ps1 — Orchestrates all scripts, generates per-script + consolidated reports, supports Windows/SQL auth, --SkipScripts, exit code 0/1
• docs/post-migration-validation.md — Usage guide, script details, common issues, integration workflow
• .gitignore — Added ValidationResults/

Testing

• I have tested these changes locally
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested the command-line interface with various scenarios

Cosmos DB Testing

• Tested with single database analysis
• Tested with multi-database analysis
• Tested report generation (Excel and Word)
• Tested with different authentication methods
• Tested error handling scenarios

Documentation

• I have updated the documentation accordingly
• I have updated the README if needed
• I have updated command-line help text if needed

Security Considerations

• No sensitive data is hardcoded
• Authentication follows Azure best practices
• No secrets in configuration files
• Dependencies are up to date and secure

All dynamic SQL uses QUOTENAME() for identifier injection prevention. PowerShell credentials use ConvertTo-SecureString.

Screenshots (if applicable)

N/A — script-only changes, no UI.

Additional Notes

Scripts are standalone SQL files runnable via sqlcmd or Invoke-Sqlcmd. The 01-RowCountValidation.sql requires populating @ExpectedCounts from the assessment report before execution. All other scripts auto-discover tables via sys.tables.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Generate post-migration validation scripts</issue_title>
<issue_description>## Description
Create automated SQL scripts to validate migration success and data integrity.

Tasks

• Row count comparison queries (Cosmos vs SQL)
• Checksum validation scripts (sample data verification)
• Sample data comparison (first/last N rows)
• Foreign key integrity checks
• Index existence validation
• Performance baseline queries
• Generate validation report template
• PowerShell script to run all validations

Generated Files

• Scripts/PostMigration/01-RowCountValidation.sql
• Scripts/PostMigration/02-DataIntegrityChecks.sql
• Scripts/PostMigration/03-SampleDataComparison.sql
• Scripts/PostMigration/04-PerformanceBaseline.sql
• Scripts/PostMigration/RunAllValidations.ps1

Acceptance Criteria

• Scripts validate all migrated tables
• Clear pass/fail results for each validation
• Automated reporting of discrepancies
• Documentation on how to run validations

Related Issues

• Depends on deps: Bump Microsoft.Extensions.Logging and Microsoft.Extensions.Logging.Console #6 (data quality checks)
• Works with Fix release pipeline by replacing deprecated GitHub Actions #10 (ADF pipeline generation)</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Generate post-migration validation scripts #68

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