[portfolio] remove SLA leakage and add reproducibility checks

[RidhanPar]

What changed

• remove resolution_hours target leakage from SLA-breach model inputs
• regenerate synthetic demo metrics after the correction
• add focused pipeline tests and GitHub Actions CI
• replace the README with concise evidence boundaries and architecture

Validation

• 4 tests passed
• corrected synthetic demo metrics: accuracy 0.8700, F1 0.9172, ROC AUC 0.8994
• compileall passed
• git diff --check passed