feat(07-01): add useWizardState hook, i18n keys, and shadcn checkbox

- Create useWizardState hook with localStorage persistence keyed by userId
- Add all setup wizard i18n keys to en.json and de.json
- Install shadcn checkbox component for step 2 item selection

src/components/ui/checkbox.tsx

@@ -0,0 +1,30 @@
+import * as React from "react"
+import { CheckIcon } from "lucide-react"
+import { Checkbox as CheckboxPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Checkbox({
+  className,
+  ...props
+}: React.ComponentProps<typeof CheckboxPrimitive.Root>) {
+  return (
+    <CheckboxPrimitive.Root
+      data-slot="checkbox"
+      className={cn(
+        "peer size-4 shrink-0 rounded-[4px] border border-input shadow-xs transition-shadow outline-none focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-destructive/20 data-[state=checked]:border-primary data-[state=checked]:bg-primary data-[state=checked]:text-primary-foreground dark:bg-input/30 dark:aria-invalid:ring-destructive/40 dark:data-[state=checked]:bg-primary",
+        className
+      )}
+      {...props}
+    >
+      <CheckboxPrimitive.Indicator
+        data-slot="checkbox-indicator"
+        className="grid place-content-center text-current transition-none"
+      >
+        <CheckIcon className="size-3.5" />
+      </CheckboxPrimitive.Indicator>
+    </CheckboxPrimitive.Root>
+  )
+}
+
+export { Checkbox }

src/hooks/useWizardState.ts

@@ -0,0 +1,85 @@
+import { useState, useEffect } from "react"
+import { PRESETS } from "@/data/presets"
+
+export interface WizardState {
+  currentStep: 1 | 2 | 3
+  income: number
+  selectedItems: Record<string, { checked: boolean; amount: number }>
+}
+
+const STORAGE_KEY = (userId: string) => `setup-wizard-${userId}`
+
+function getDefaultState(): WizardState {
+  const selectedItems: Record<string, { checked: boolean; amount: number }> = {}
+  for (const preset of PRESETS) {
+    selectedItems[preset.slug] = {
+      checked: preset.type === "bill" || preset.type === "variable_expense",
+      amount: preset.defaultAmount,
+    }
+  }
+  return { currentStep: 1, income: 3000, selectedItems }
+}
+
+export function useWizardState(userId: string) {
+  const [state, setState] = useState<WizardState>(() => {
+    try {
+      const saved = localStorage.getItem(STORAGE_KEY(userId))
+      if (saved) {
+        const parsed = JSON.parse(saved)
+        // Validate shape (T-07-01 mitigation: validate JSON on load)
+        if (
+          parsed &&
+          typeof parsed.currentStep === "number" &&
+          parsed.currentStep >= 1 &&
+          parsed.currentStep <= 3 &&
+          typeof parsed.income === "number" &&
+          parsed.income >= 0 &&
+          parsed.selectedItems &&
+          typeof parsed.selectedItems === "object"
+        ) {
+          return parsed as WizardState
+        }
+      }
+    } catch {
+      /* ignore corrupt data */
+    }
+    return getDefaultState()
+  })
+
+  useEffect(() => {
+    localStorage.setItem(STORAGE_KEY(userId), JSON.stringify(state))
+  }, [state, userId])
+
+  const setStep = (step: 1 | 2 | 3) =>
+    setState((s) => ({ ...s, currentStep: step }))
+
+  const setIncome = (income: number) =>
+    setState((s) => ({ ...s, income }))
+
+  const toggleItem = (slug: string) =>
+    setState((s) => ({
+      ...s,
+      selectedItems: {
+        ...s.selectedItems,
+        [slug]: {
+          ...s.selectedItems[slug],
+          checked: !s.selectedItems[slug].checked,
+        },
+      },
+    }))
+
+  const setItemAmount = (slug: string, amount: number) =>
+    setState((s) => ({
+      ...s,
+      selectedItems: {
+        ...s.selectedItems,
+        [slug]: { ...s.selectedItems[slug], amount },
+      },
+    }))
+
+  const clearState = () => {
+    localStorage.removeItem(STORAGE_KEY(userId))
+  }
+
+  return { state, setStep, setIncome, toggleItem, setItemAmount, clearState }
+}

src/i18n/de.json

@@ -121,6 +121,44 @@
     "error": "Etwas ist schiefgelaufen",
     "confirm": "Bestätigen"
   },
+  "setup": {
+    "title": "Budget einrichten",
+    "step1": {
+      "title": "Monatliches Einkommen",
+      "description": "Wie viel verdienst du pro Monat?",
+      "incomeLabel": "Monatliches Nettoeinkommen",
+      "helper": "Gib dein monatliches Nettoeinkommen ein",
+      "validation": "Bitte gib einen positiven Betrag ein"
+    },
+    "step2": {
+      "title": "Wiederkehrende Posten",
+      "description": "Wähle deine regelmäßigen monatlichen Ausgaben",
+      "remaining": "Verbleibend zu verteilen"
+    },
+    "step3": {
+      "title": "Übersicht",
+      "description": "Bestätige deine Budgetvorlage",
+      "incomeLabel": "Monatliches Einkommen",
+      "totalLabel": "Gesamtausgaben",
+      "remainingLabel": "Verbleibend",
+      "empty": "Keine Posten ausgewählt. Du kannst später Posten zu deiner Vorlage hinzufügen."
+    },
+    "steps": {
+      "1": "Einkommen",
+      "2": "Posten",
+      "3": "Übersicht"
+    },
+    "next": "Nächster Schritt",
+    "back": "Zurück",
+    "skip": "Schritt überspringen",
+    "skipSetup": "Einrichtung überspringen",
+    "complete": "Einrichtung abschließen",
+    "toast": {
+      "success": "Vorlage erstellt! Dein erstes Budget wird automatisch erscheinen.",
+      "error": "Vorlage konnte nicht gespeichert werden. Bitte versuche es erneut.",
+      "partialError": "Einige Posten konnten nicht gespeichert werden. Prüfe deine Vorlagenseite."
+    }
+  },
   "presets": {
     "income": {
       "salary": "Gehalt",

src/i18n/en.json

@@ -121,6 +121,44 @@
     "error": "Something went wrong",
     "confirm": "Confirm"
   },
+  "setup": {
+    "title": "Set up your budget",
+    "step1": {
+      "title": "Monthly Income",
+      "description": "How much do you earn each month?",
+      "incomeLabel": "Monthly net income",
+      "helper": "Enter your total monthly take-home pay",
+      "validation": "Please enter a positive income amount"
+    },
+    "step2": {
+      "title": "Recurring Items",
+      "description": "Select your regular monthly expenses",
+      "remaining": "Remaining to allocate"
+    },
+    "step3": {
+      "title": "Review",
+      "description": "Confirm your budget template",
+      "incomeLabel": "Monthly income",
+      "totalLabel": "Total expenses",
+      "remainingLabel": "Remaining",
+      "empty": "No items selected. You can add items to your template later."
+    },
+    "steps": {
+      "1": "Income",
+      "2": "Items",
+      "3": "Review"
+    },
+    "next": "Next Step",
+    "back": "Go Back",
+    "skip": "Skip Step",
+    "skipSetup": "Skip setup",
+    "complete": "Complete Setup",
+    "toast": {
+      "success": "Template created! Your first budget will appear automatically.",
+      "error": "Could not save your template. Please try again.",
+      "partialError": "Some items could not be saved. Check your template page."
+    }
+  },
   "presets": {
     "income": {
       "salary": "Salary",