docs: add Phase 2 design decisions and session orientation

[Kilbas]

Summary

This PR adds comprehensive documentation for Phase 2 (Outbound Email Engine) and establishes session orientation guides for future development work. No application code changes are included.

Key Changes

• docs/product/PHASE_2_PRODUCT_DECISIONS.md — Finalized design decisions for Phase 2, covering:

  • Contact bucket state machine (cold → first_sent → replied → etc.)
  • LLM email generation with Claude, retry logic, and per-member calibration
  • Review queue workflow (approve, edit+approve, reject, inline AI refinement)
  • Bulk send architecture (BullMQ + Redis worker)
  • Per-member SMTP configuration and error handling
  • Tracking pixel (workspace-level toggle)
  • Brief model for campaign configuration
  • Infrastructure additions (Redis, worker process)

• docs/product/PHASES.md — Phase roadmap documenting scope and status for all six planned phases, with contact bucket state transitions and infrastructure requirements per phase

• docs/product/PRODUCT_VISION.md — High-level product vision, target users, core problem/solution, deployment model (self-hosted single-tenant), and design principles

• docs/ai/START_HERE.md — New session orientation guide covering project overview, current status, key documents, codebase structure, tech stack, roles, and quick-start commands

• docs/ai/TASK_RUNBOOK.md — Detailed runbook for Claude Code sessions, including orientation checklist, branch conventions, task pickup process, commit conventions, code conventions, testing strategy, and infrastructure change guidelines

• docs/ai/SESSION_HANDOFF.md — Session state tracking document recording Phase 1 completion, Phase 2 planned scope, what was done in the last session, next steps, and known gotchas

Notable Details

• All Phase 2 design decisions are marked as final and approved; implementation should not deviate without explicit product owner instruction
• Contact bucket transitions have strict rules enforced at import, send, and UI levels
• Rate limiting defaults to 50 emails/day/member but is configurable per workspace
• Calibration activates after 100 approved+edited emails per member
• Documentation establishes clear conventions for commits, code organization, testing, and infrastructure changes to guide future development

https://claude.ai/code/session_018RdP4HdHLxkTwrpsjyTzJu