Add Track B instruction doc: Helm chart and session automation

Detailed specification for Claude Code covering:
- Helm chart structure (charts/baft/) with values.yaml design
- Framework git-sync architecture (git-sync + commit-agent sidecars)
- Session CLI commands (baft session start/end/status/sync-check/sync)
- Session MCP tools for Claude Chat integration
- Environment prerequisite checker (baft preflight)
- Phased implementation sequence with testing strategy

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hooman