Use CPMigrate in CI with JSON-only output and stable exit codes

Infrastructure teams do not need another hand-parsed CLI. CPMigrate already supports JSON output, quiet mode, dependency analysis, and exit codes suitable for gates and scheduled checks.

cpmigrate --analyze --audit --outdated --deprecated --output Json --quiet > analysis.json

- name: Install CPMigrate
  run: dotnet tool install --global CPMigrate

- name: Analyze dependency health
  run: cpmigrate --analyze --audit --outdated --deprecated --output Json --quiet > analysis.json