[Backend] Add CFACTS model functions for system comparison queries

[danielbowne]

Overview

Add model layer functions to query CFACTS data and compare with ZTMF systems. This provides the data logic layer for the API endpoints.

Parent Epic: #233

Customer Value

Backend can find discrepancies between SDL CFACTS data and ZTMF systems programmatically.

Scope

Create backend/internal/model/cfacts.go with:

Functions to Implement

1. FindCFACTSSystems() - Query cfacts_systems table with filters

   • Support filters: is_active, is_retired, is_decommissioned
   • Pagination support
   • Return CFACTS system data

2. CompareWithZTMF() - JOIN query to find matches/mismatches

   • FULL OUTER JOIN: fismasystems ↔ cfacts_systems
   • Match on fisma_uuid = fismauid
   • Return side-by-side comparison

3. FindDiscrepancies() - Categorize data quality issues

   • Systems in CFACTS but missing from ZTMF
   • Systems in ZTMF but missing from CFACTS
   • ISSO email mismatches
   • Decommission status conflicts
   • Return categorized discrepancy list

Patterns to Follow

• Reuse patterns from fismasystems.go
• Use squirrel query builder
• Use pgx for database access
• Consistent error handling

Acceptance Criteria

• Model file created: backend/internal/model/cfacts.go
• All 3 query functions implemented
• Unit tests for each function
• Test coverage > 80%
• Works with test data: _test_data_cfacts_empire.sql
• Code comments document each function
• Follows existing codebase patterns

Testing

# Run unit tests
make test-unit

# Run with coverage
make test-coverage

Size Estimate

Small (1-2 days)

Dependencies

• Table exists (Issue #XXX completed)
• Test data exists (PR Stage 1: Add cfacts_systems table for SDL CFACTS sync #240)

Blocks

• Issue #XXX (API endpoints need this model layer)

Related

• Parent: [Epic] Sync FISMA system data from SDL CFACTS tables #233 (SDL/CFACTS Sync Epic)
• Depends on: Database table (already complete)
• Blocks: API endpoints