fix(routing): finish /home migration in WelcomeStep3 + VerifyEmailPage

The original public-landing routing refactor migrated WelcomeRouter,
WelcomeStep1, and WelcomeStep2 post-onboarding redirects to /home, but
left four sites still pointing at the old / + query-string destinations:

  - WelcomeStep3 `completeWizardAndExit` (Send invites)
  - WelcomeStep3 `handleSkipStep` (Skip)
  - VerifyEmailPage post-verify auto-redirect (`setTimeout`)
  - VerifyEmailPage success-state "Go to dashboard" Link

These all worked by accident because PublicLanding redirects authed
users from / to /home — so users still landed on the dashboard, but
through an unnecessary mount-and-redirect flicker, and the
`?welcome=true` / `?verified=1` query markers got dropped on the way.

Drop both query markers — neither is read anywhere in the codebase
(grepped frontend/src; the dashboard's onboarding UX is driven by
`getOnboardingStatus`, not URL state). Carrying dead URL params
just invites future "is this load-bearing?" investigations.

Test stubs in WelcomeStep3.test.tsx and VerifyEmailPage.test.tsx
moved from `<Route path="/">` to `<Route path="/home">` so the
assertions verify the new destination instead of accidentally matching
the old one (the previous stubs masked the partial migration).

Out of scope: AcceptInvitePage and OAuthCallbackPage still use
`?welcome=teammate`, but that one carries an explicit "decoded by the
dashboard in Task 41" annotation and may be wired up later, so left
untouched.

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

frontend/src/pages/VerifyEmailPage.tsx

@@ -20,8 +20,7 @@ const SUCCESS_REDIRECT_MS = 1200
  *   "Already verified" state. No API call.
  * - Else fire `POST /auth/email/verify` exactly once (a `useRef` guard keeps
  *   React 19 strict-mode double-invoke from double-firing the call). On
- *   success, refresh the auth store and bounce to `/?verified=1` so the
- *   dashboard surfaces a toast.
+ *   success, refresh the auth store and bounce to `/home`.
  * - On error, show "Invalid or expired token" + a "Resend" CTA that calls
  *   `POST /auth/email/send-verification`.
  */
@@ -70,10 +69,9 @@ export function VerifyEmailPage() {
         if (cancelled) return
         setStatus('success')
         toast.success('Email verified')
-        // Brief success state, then redirect with a query flag so the
-        // dashboard can re-surface confirmation if it wants to.
+        // Brief success state, then redirect to the dashboard.
         window.setTimeout(() => {
-          navigate('/?verified=1', { replace: true })
+          navigate('/home', { replace: true })
         }, SUCCESS_REDIRECT_MS)
       })
       .catch((err) => {
@@ -126,7 +124,7 @@ export function VerifyEmailPage() {
                 Redirecting you to the dashboard…
               </p>
               <Link
-                to="/?verified=1"
+                to="/home"
                 replace
                 className={cn(
                   'mt-6 inline-flex items-center rounded-lg bg-primary px-6 py-2 text-sm font-semibold text-primary-foreground',