Persist values, tighten validation, and a11y on /onboarding

- Server action echoes kitaName, the three module booleans, and the
  Mindest-Verfügbarkeiten value on every error path so failed submits no
  longer wipe what the user typed; OnboardingState gains an `attempt`
  counter that drives a per-field remount key on the client.
- Schema now rejects min=0 when the Notdienst module is active (via
  superRefine) — previously a kita could be created with 0 minimum days,
  which is fachlich sinnlos. When the module is off, 0 stays valid.
- Validation error messages reworded from terse fragments ("Nicht
  negativ.", "Bitte ganze Zahl.") to full sentences.
- Field error <p> elements gain role="alert" + aria-live="polite" so
  screen readers announce them on submit.
- CardTitle now accepts as="h1" and the onboarding page uses it for
  "Willkommen, …" — the page now has a real top-level heading.
- ModuleCheckbox uses aria-labelledby + aria-describedby so the
  accessible name is just the module title; the longer description is
  exposed as secondary info instead of being concatenated into the AN.

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

src/app/onboarding/actions.ts

@@ -16,21 +16,35 @@ import { prisma } from "@/lib/prisma";
 // — kein "halb-eingerichteter" Zwischenzustand.
 // =====================================================================
 
-const onboardingSchema = z.object({
-  kitaName: z
-    .string()
-    .min(2, "Mindestens 2 Zeichen.")
-    .max(120, "Maximal 120 Zeichen.")
-    .trim(),
-  notdienstModuleEnabled: z.preprocess(checkboxToBool, z.boolean()),
-  terminModuleEnabled: z.preprocess(checkboxToBool, z.boolean()),
-  adressbuchModuleEnabled: z.preprocess(checkboxToBool, z.boolean()),
-  notdienstMinPerChildPerMonth: z.coerce
-    .number()
-    .int("Bitte ganze Zahl.")
-    .min(0, "Nicht negativ.")
-    .max(31, "Maximal 31 Tage pro Monat."),
-});
+const onboardingSchema = z
+  .object({
+    kitaName: z
+      .string()
+      .trim()
+      .min(2, "Bitte mindestens 2 Zeichen angeben.")
+      .max(120, "Maximal 120 Zeichen."),
+    notdienstModuleEnabled: z.preprocess(checkboxToBool, z.boolean()),
+    terminModuleEnabled: z.preprocess(checkboxToBool, z.boolean()),
+    adressbuchModuleEnabled: z.preprocess(checkboxToBool, z.boolean()),
+    notdienstMinPerChildPerMonth: z.coerce
+      .number()
+      .int("Bitte eine ganze Zahl angeben.")
+      .min(0, "Bitte einen Wert von 0 oder mehr angeben.")
+      .max(31, "Maximal 31 Tage pro Monat."),
+  })
+  .superRefine((data, ctx) => {
+    // Mindest-Verfügbarkeit nur relevant, wenn das Notdienst-Modul aktiv ist.
+    // Bei aktivem Modul muss mindestens 1 Tag eingetragen sein — 0 wäre
+    // fachlich sinnlos und würde den Planer leerlaufen lassen.
+    if (data.notdienstModuleEnabled && data.notdienstMinPerChildPerMonth < 1) {
+      ctx.addIssue({
+        path: ["notdienstMinPerChildPerMonth"],
+        code: "custom",
+        message:
+          "Bei aktivem Notdienst-Modul: mindestens 1 Tag pro Monat angeben.",
+      });
+    }
+  });
 
 function checkboxToBool(value: unknown): boolean {
   // HTML-Checkbox: "on" wenn aktiviert, sonst nicht im FormData.
@@ -38,6 +52,17 @@ function checkboxToBool(value: unknown): boolean {
 }
 
 export type OnboardingState = {
+  // Bumped after every action call so the client can key uncontrolled inputs
+  // and force a remount with the echoed values from a failed submit.
+  attempt: number;
+  // Echoed inputs so a failed submit doesn't wipe the form.
+  values?: {
+    kitaName?: string;
+    notdienstModuleEnabled?: boolean;
+    terminModuleEnabled?: boolean;
+    adressbuchModuleEnabled?: boolean;
+    notdienstMinPerChildPerMonth?: number;
+  };
   errors?: {
     kitaName?: string[];
     notdienstMinPerChildPerMonth?: string[];
@@ -45,10 +70,25 @@ export type OnboardingState = {
   };
 };
 
+export const initialOnboardingState: OnboardingState = { attempt: 0 };
+
+function echoValues(formData: FormData): OnboardingState["values"] {
+  const min = formData.get("notdienstMinPerChildPerMonth");
+  return {
+    kitaName: String(formData.get("kitaName") ?? ""),
+    notdienstModuleEnabled: formData.get("notdienstModuleEnabled") === "on",
+    terminModuleEnabled: formData.get("terminModuleEnabled") === "on",
+    adressbuchModuleEnabled: formData.get("adressbuchModuleEnabled") === "on",
+    notdienstMinPerChildPerMonth:
+      min === null || min === "" ? undefined : Number(min),
+  };
+}
+
 export async function completeOnboardingAction(
-  _prev: OnboardingState,
+  prev: OnboardingState,
   formData: FormData,
 ): Promise<OnboardingState> {
+  const attempt = prev.attempt + 1;
   const session = await auth();
   if (!session?.user) {
     redirect("/login");
@@ -61,7 +101,11 @@ export async function completeOnboardingAction(
 
   const parsed = onboardingSchema.safeParse(Object.fromEntries(formData));
   if (!parsed.success) {
-    return { errors: parsed.error.flatten().fieldErrors };
+    return {
+      attempt,
+      values: echoValues(formData),
+      errors: parsed.error.flatten().fieldErrors,
+    };
   }
   const data = parsed.data;
 
@@ -99,6 +143,8 @@ export async function completeOnboardingAction(
     }
     if (err instanceof Prisma.PrismaClientKnownRequestError) {
       return {
+        attempt,
+        values: echoValues(formData),
         errors: { _form: ["Datenbankfehler — bitte erneut versuchen."] },
       };
     }