feat: inventory reconciliation – data comparison, quality checks, and test suite

[shahvarun93]

Title:

feat: inventory reconciliation – data comparison, quality checks, and test suite

Description:

## Summary
Implements the inventory reconciliation assessment against the two provided CSV snapshots.

## Deliverables
- `reconcile.py` – loads both snapshots, normalises data, reconciles differences, and outputs structured reports
- `tests/test_reconcile.py` – 39 pytest cases covering normalisation helpers, snapshot loading, and reconciliation logic
- `output/` – CSV and JSON reports generated against the actual snapshot data
- `NOTES.md` – approach, data quality findings, and AI tooling usage

## Reconciliation Results
| Status | Count |
|---|---|
| Quantity changed | 71 |
| Added (new) | 5 |
| Removed | 2 |
| Unchanged | 2 |

## Data Quality Issues Found
- Non-standard SKU formats (`SKU005`, `sku-008`) → normalised
- Duplicate SKU-045 in snapshot 2 with conflicting name and negative quantity
- Mismatched column names between snapshots (`qty` vs `quantity`, etc.) → handled via column alias map
- Float quantities (`70.0`, `80.00`) and non-ISO date format (`01/15/2024`) → normalised
- Leading/trailing whitespace in names and locations → stripped

## How to Run
```bash
python reconcile.py
python -m pytest tests/ -v