Add unit tests for ReportManager.reconstruct() edge cases

[himanshu231204]

Description

The \ReportManager.reconstruct()\ method in \openagent_eval/reports/manager.py\ silently creates a default Config when the config section is missing. This should be tested, along with other edge cases.

What to Test

• 
  econstruct()\ with a complete report JSON
• 
  econstruct()\ with missing config section (should it raise an error or use defaults?)
• 
  econstruct()\ with malformed data
• 
  econstruct()\ with missing required fields

Files to Look At

• \openagent_eval/reports/manager.py\ — the implementation
• \openagent_eval/reports/base.py\ — base report classes
• \ ests/unit/test_reports/\ — existing report tests

Suggested Approach

Add tests to \ ests/unit/test_reports/test_base.py\ or create a new \ est_manager.py\ file.

Good First Issue ✅

Focused testing task with clear edge cases to cover.