Phase 7: Add user onboarding tour and tenant setup wizard

Feature 1 - How-To Intro Tour (react-joyride):
- 8-step guided walkthrough highlighting Dashboard, Accounts, Assessments,
  Transactions, Budgets, Reports, and AI Investment Planning
- Runs automatically on first login, tracked via has_seen_intro flag on user
- Centralized step config in config/tourSteps.ts for easy text editing
- data-tour attributes on Sidebar nav items and Dashboard for targeting

Feature 2 - Tenant Onboarding Wizard:
- 3-step modal wizard: create operating account, assessment group + units,
  import budget CSV
- Runs after tour completes, tracked via onboardingComplete in org settings JSONB
- Reuses existing API endpoints (POST /accounts, /assessment-groups, /units,
  /budgets/:year/import)

Backend changes:
- Add has_seen_intro column to shared.users + migration
- Add PATCH /auth/intro-seen endpoint to mark tour complete
- Add PATCH /organizations/settings endpoint for org settings updates
- Include hasSeenIntro in login response, settings in switch-org response

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

db/migrations/009-onboarding-flags.sql

@@ -0,0 +1,9 @@
+-- Migration: Add onboarding tracking flag to users table
+-- Phase 7: Onboarding Features
+
+BEGIN;
+
+ALTER TABLE shared.users
+  ADD COLUMN IF NOT EXISTS has_seen_intro BOOLEAN DEFAULT FALSE;
+
+COMMIT;