docs: phase 1 implementation plan for sec-fix-pipeline skeleton

End-to-end plumbing plan — new repo at ~/Development/sec-fix-pipeline/,
worker daemon, stub agent container, MinIO artifact storage, Linear
label state machine. Stub agent only; Phases 2-6 (real agent, full
stack, durability, resumable runs, dashboard) tracked separately.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: d-cs