fix: preserve URL hash and OIDC redirect target through login flow

- Include location.hash in redirect param at all three producer sites
  (ProtectedRoute, axios 401 interceptor, OAuthAuthorizePage) so
  hash fragments survive the login bounce
- Stash redirectTarget in sessionStorage before any OIDC provider
  redirect and restore it after the code exchange, since the IdP
  strips the original ?redirect= param during the roundtrip
- Clear sessionStorage on OIDC error to avoid stale state
- Add tests covering sessionStorage stash on mount, navigate to saved
  redirect after OIDC exchange, fallback to /dashboard, and cleanup
  on error

client/src/api/client.ts

@@ -75,7 +75,7 @@ apiClient.interceptors.response.use(
     if (error.response?.status === 401 && (error.response?.data as { code?: string } | undefined)?.code === 'AUTH_REQUIRED') {
       const { pathname } = window.location
       if (!isAuthPublicPath(pathname)) {
-        const currentPath = pathname + window.location.search
+        const currentPath = pathname + window.location.search + window.location.hash
         window.location.href = '/login?redirect=' + encodeURIComponent(currentPath)
       }
     }