feat(onboarding): add welcome wizard scaffold + Step 1 (Your shop)

Lays the groundwork for the post-signup welcome wizard (Phase 2,
Task 38). Authed users hitting /welcome are routed to the next
incomplete step based on users.onboarding_step_completed +
users.onboarding_dismissed; refresh resumes correctly because every
navigation persists state server-side first.

Backend:
- Expose onboarding_step_completed (Optional[int]) and
  onboarding_dismissed (bool) on UserResponse so /auth/me drives
  client-side routing without a separate fetch.

Frontend:
- WelcomeRouter handles the /welcome decision table (dismissed → /,
  completed >=3 → /, else next step).
- WelcomeStep1 renders the "Your shop" form (company name pre-filled
  from accounts.name, team size 1-2/3-5/6-10/11-25/26+, role
  Owner/Lead Tech/Tech/Other). Continue PATCHes /users/me/onboarding-step
  with action=complete; Skip-this-step PATCHes action=skip; Skip-the-rest
  POSTs /users/me/onboarding-dismiss-rest. Each action refreshes the
  auth store before navigating so the router resumes correctly on the
  next visit.
- onboardingApi.updateStep + dismissRest (typed against backend
  OnboardingStepRequest/Response schemas).
- Routes mounted inside AppLayout so EmailVerificationBanner persists
  above each step per spec.
- 11 vitest cases covering the routing decision table + Continue / Skip
  / Skip-the-rest / persist-failure paths.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/api/onboarding.ts

@@ -19,3 +19,51 @@ export async function getOnboardingStatus(): Promise<OnboardingStatus> {
 export async function dismissOnboarding(): Promise<void> {
   await apiClient.post('/users/onboarding-status/dismiss')
 }
+
+// --- Welcome wizard (Phase 2) ---------------------------------------------
+
+export type WizardStep = 1 | 2 | 3
+export type WizardAction = 'complete' | 'skip'
+export type TeamSizeBucket = '1-2' | '3-5' | '6-10' | '11-25' | '26+'
+export type RoleAtSignup = 'owner' | 'lead_tech' | 'tech' | 'other'
+export type PrimaryPsa = 'connectwise' | 'autotask' | 'halopsa' | 'none'
+
+export interface OnboardingStepData {
+  // Step 1
+  company_name?: string
+  team_size_bucket?: TeamSizeBucket
+  role_at_signup?: RoleAtSignup
+  // Step 2
+  primary_psa?: PrimaryPsa
+}
+
+export interface OnboardingStepRequest {
+  step: WizardStep
+  action: WizardAction
+  data?: OnboardingStepData
+}
+
+export interface OnboardingStepResponse {
+  onboarding_step_completed: number | null
+  onboarding_dismissed: boolean
+}
+
+export const onboardingApi = {
+  getStatus: getOnboardingStatus,
+  dismiss: dismissOnboarding,
+  /** Persist welcome-wizard progress for the current user. */
+  async updateStep(payload: OnboardingStepRequest): Promise<OnboardingStepResponse> {
+    const response = await apiClient.patch<OnboardingStepResponse>(
+      '/users/me/onboarding-step',
+      payload,
+    )
+    return response.data
+  },
+  /** Skip the rest of the welcome wizard — sets users.onboarding_dismissed=TRUE. */
+  async dismissRest(): Promise<OnboardingStepResponse> {
+    const response = await apiClient.post<OnboardingStepResponse>(
+      '/users/me/onboarding-dismiss-rest',
+    )
+    return response.data
+  },
+}