docs: update CHANGELOG with Tenant Isolation Phase 2 and Phase 3 details

- Document Phase 2: PostgreSQL RLS on 11 session tables, account_id NOT NULL enforcement, Alembic migration support
- Document Phase 3: RLS on audit_logs and tree_shares, cross-tenant session access for public shares, complete account_id propagation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CHANGELOG.md

@@ -9,6 +9,8 @@ All notable changes to ResolutionFlow are documented here.
 - Recurring Issue Detection — client-specific pattern alerts (#60)
 - Step Feedback Flag — "This Step is Wrong" reporting (#58)
 - **Tenant Isolation Phase 0** — multi-tenant data isolation (#132) with app-layer filtering helpers (`tenant_filter()`, `get_tenant_context`), cross-tenant access audit (analytics, categories, AI sessions, trees), UUID endpoint isolation with 404 responses for unauthorized access, ownership checks on all sensitive operations, and CI grep gate for missing tenant filters
+- **Tenant Isolation Phase 2** — PostgreSQL Row Level Security (RLS) on 11 session-related tables (ai_sessions, session_steps, session_tags, etc.), account_id NOT NULL enforcement on all write paths, Alembic migrations with dual-env support (Railway native vars + explicit DATABASE_URL_SYNC), RLS test coverage with cross-account isolation verification, migration CI/CD integration
+- **Tenant Isolation Phase 3** — RLS on audit_logs and tree_shares tables, cross-tenant session access for public shares (via get_admin_db), complete account_id propagation across PSA integration write paths, final RLS policy enforcement
 - **Script Library default view** — "All Scripts" tab now displays all accessible scripts (team + library)
 - **Session documentation overhaul** — reformatted PSA resolution/escalation notes with cleaner headers, inline engineer responses, decimal hour display (0.25 hrs), follow-up recommendations, and improved "What We Know" section from evidence items
 - **Client communication improvements** — new `request_info` audience type for client-facing information requests, improved status update and email draft prompts with per-context guidance