feat: Implement comprehensive onboarding improvements with role-based family invites

This commit adds a complete onboarding improvements system including progress
tracking, streamlined UI, and role-based family invitation system.

## Backend Changes

### Database Migrations
- Add onboarding tracking fields to users table (onboarding_completed, onboarding_step, onboarding_data)
- Add role-based invite codes to families table (parent/caregiver/viewer codes with expiration)
- Add indexes for fast invite code lookups

### User Preferences Module
- Add UserPreferencesController with onboarding endpoints
- Add UserPreferencesService with progress tracking methods
- Add UpdateOnboardingProgressDto for validation
- Endpoints: GET/PUT /api/v1/preferences/onboarding, POST /api/v1/preferences/onboarding/complete

### Families Module - Role-Based Invites
- Add generateRoleInviteCode() - Generate role-specific codes with expiration
- Add getRoleInviteCodes() - Retrieve all active codes for a family
- Add joinFamilyWithRoleCode() - Join family with automatic role assignment
- Add revokeRoleInviteCode() - Revoke specific role invite codes
- Add sendEmailInvite() - Generate code and send email invitation
- Endpoints: POST/GET/DELETE /api/v1/families/:id/invite-codes, POST /api/v1/families/join-with-role, POST /api/v1/families/:id/email-invite

### Email Service
- Add sendFamilyInviteEmail() - Send role-based invitation emails
- Beautiful HTML templates with role badges (👨‍👩‍👧 parent, 🤝 caregiver, 👁️ viewer)
- Role-specific permission descriptions
- Graceful fallback if email sending fails

### Auth Service
- Fix duplicate family creation bug in joinFamily()
- Ensure users only join family once during onboarding

## Frontend Changes

### Onboarding Page
- Reduce steps from 5 to 4 (combined language + measurements)
- Replace card-based selection with dropdown selectors
- Add automatic progress saving after each step
- Add progress restoration on page mount
- Extract FamilySetupStep into reusable component

### Family Page
- Add RoleInvitesSection component with accordion UI
- Generate/view/copy/regenerate/revoke controls for each role
- Send email invites directly from UI
- Display expiration dates (e.g., "Expires in 5 days")
- Info tooltips explaining role permissions
- Only visible to users with parent role

### API Client
- Add role-based invite methods to families API
- Add onboarding progress methods to users API
- TypeScript interfaces for all new data structures

## Features

✅ Streamlined 4-step onboarding with dropdown selectors
✅ Automatic progress save/restore across sessions
✅ Role-based family invites (parent/caregiver/viewer)
✅ Beautiful email invitations with role descriptions
✅ Automatic role assignment when joining with invite codes
✅ Granular permission control per role
✅ Email fallback if sending fails
✅ All changes tested and production-ready

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

maternal-web/app/family/page.tsx

@@ -34,6 +34,7 @@ import { familiesApi, Family, FamilyMember, InviteMemberData, JoinFamilyData } f
 import { InviteMemberDialog } from '@/components/family/InviteMemberDialog';
 import { JoinFamilyDialog } from '@/components/family/JoinFamilyDialog';
 import { RemoveMemberDialog } from '@/components/family/RemoveMemberDialog';
+import { RoleInvitesSection } from '@/components/family/RoleInvitesSection';
 import { motion } from 'framer-motion';
 import { useTranslation } from '@/hooks/useTranslation';
 import { useSelectedFamily } from '@/hooks/useSelectedFamily';
@@ -427,6 +428,17 @@ export default function FamilyPage() {
                     )}
                   </Paper>
               </Grid>
+
+              {/* Role-Based Invites - Only visible to parents */}
+              {isParent && family && (
+                <Grid item xs={12}>
+                  <RoleInvitesSection
+                    familyId={familyId!}
+                    onSuccess={(message) => setSnackbar({ open: true, message })}
+                    onError={(message) => setError(message)}
+                  />
+                </Grid>
+              )}
             </Grid>
           )}
         </Container>