[EPIC] Core Scanning Engine

**Product Line**: B2B | **Phase**: MVP | **Priority**: P0 | **Estimate**: 21 pts

## User Story
*As a DevOps engineer, I want to scan my local codebase for PII without uploading it to the cloud, so that I can maintain data sovereignty.*

## Success Metrics
- Scans 1000 files in < 30 seconds
- Detects SSN, emails, credit cards, API keys
- Zero data egress

## Tasks
Will be broken down into user stories.

No files, tests, or entry points are mentioned. This is an epic whose work is explicitly deferred to future user stories; use those stories to identify the implementation and verification scope, with completion measured against the listed scan speed, detection, and zero-egress metrics.

索引モデルが issue の本文から書いたものです。