feat: add category management page (create/edit/delete)

The backend already had full category CRUD but nothing in the UI exposed
it — categories could only be viewed inside charts. Adds a Categories nav
item and page with icon/color pickers, grouped by expense/income, backed
by new create/update/delete mutations. Also expands icons.tsx's ICON_MAP,
which was missing 14 icon keys already in use by real category data and
silently falling back to a wallet glyph everywhere they render.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/lib/i18n.ts

@@ -10,6 +10,7 @@ const ru = {
   "nav.roi": "Доходность",
   "nav.transactions": "Транзакции",
   "nav.accounts": "Счета",
+  "nav.categories": "Категории",
   "nav.cashFlow": "Движение денег",
   "nav.reports": "Отчёты",
   "nav.budget": "Бюджет",
@@ -300,6 +301,24 @@ const ru = {
   "account.form.typeLabel": "Тип",
   "account.form.saveError": "Не удалось сохранить счёт. Проверьте данные и попробуйте снова.",
 
+  "category.expenseSectionTitle": "Категории расходов",
+  "category.incomeSectionTitle": "Категории доходов",
+  "category.empty": "Категорий пока нет.",
+  "category.defaultBadge": "стандартная",
+  "category.defaultCannotDelete": "Стандартные категории нельзя удалить",
+  "category.confirmDelete": "Удалить категорию «{{name}}»?\n\nЕё транзакции останутся без категории.",
+  "category.kind.expense": "Расход",
+  "category.kind.income": "Доход",
+  "category.form.newTitle": "Новая категория",
+  "category.form.editTitle": "Изменить категорию",
+  "category.form.nameLabel": "Название",
+  "category.form.namePlaceholder": "Продукты, транспорт, подписки…",
+  "category.form.kindLabel": "Тип",
+  "category.form.iconLabel": "Иконка",
+  "category.form.colorLabel": "Цвет",
+  "category.form.customColorLabel": "Свой цвет",
+  "category.form.saveError": "Не удалось сохранить категорию. Проверьте данные и попробуйте снова.",
+
   "cashFlow.income": "Доход",
   "cashFlow.expense": "Расход",
   "cashFlow.net": "Баланс",
@@ -344,6 +363,7 @@ const en: Record<keyof typeof ru, string> = {
   "nav.roi": "Returns",
   "nav.transactions": "Transactions",
   "nav.accounts": "Accounts",
+  "nav.categories": "Categories",
   "nav.cashFlow": "Cash Flow",
   "nav.reports": "Reports",
   "nav.budget": "Budget",
@@ -634,6 +654,24 @@ const en: Record<keyof typeof ru, string> = {
   "account.form.typeLabel": "Type",
   "account.form.saveError": "Failed to save the account. Check the data and try again.",
 
+  "category.expenseSectionTitle": "Expense categories",
+  "category.incomeSectionTitle": "Income categories",
+  "category.empty": "No categories yet.",
+  "category.defaultBadge": "default",
+  "category.defaultCannotDelete": "Default categories cannot be deleted",
+  "category.confirmDelete": "Delete the category “{{name}}”?\n\nIts transactions will be left uncategorized.",
+  "category.kind.expense": "Expense",
+  "category.kind.income": "Income",
+  "category.form.newTitle": "New category",
+  "category.form.editTitle": "Edit category",
+  "category.form.nameLabel": "Name",
+  "category.form.namePlaceholder": "Groceries, transport, subscriptions…",
+  "category.form.kindLabel": "Type",
+  "category.form.iconLabel": "Icon",
+  "category.form.colorLabel": "Color",
+  "category.form.customColorLabel": "Custom color",
+  "category.form.saveError": "Failed to save the category. Check the data and try again.",
+
   "cashFlow.income": "Income",
   "cashFlow.expense": "Expense",
   "cashFlow.net": "Net",

frontend/src/lib/icons.tsx

@@ -5,25 +5,41 @@ import {
   Building2,
   Car,
   Clapperboard,
+  Code,
+  Dumbbell,
+  Gamepad2,
   Gem,
   Gift,
+  GraduationCap,
   HeartPulse,
   Home,
   MoreHorizontal,
   Package,
+  Plane,
   PlusCircle,
+  Receipt,
   Repeat,
+  Shapes,
+  Shirt,
   ShoppingBag,
   ShoppingBasket,
+  Smartphone,
+  Sofa,
+  Sparkles,
   TrendingUp,
+  Truck,
   Utensils,
+  Video,
   Wallet,
+  ZapOff,
   type LucideIcon,
 } from "lucide-react";
 
 // Maps the backend's plain-string icon keys (Category.icon) to a concrete
 // lucide component. New categories fall back to a generic wallet glyph so an
-// unmapped icon key never breaks rendering.
+// unmapped icon key never breaks rendering. Keep this in sync with whatever
+// icon keys actually exist on Category rows — an icon used by a real
+// category but missing here silently renders as the Wallet fallback.
 const ICON_MAP: Record<string, LucideIcon> = {
   home: Home,
   "shopping-basket": ShoppingBasket,
@@ -44,9 +60,29 @@ const ICON_MAP: Record<string, LucideIcon> = {
   "building-2": Building2,
   package: Package,
   gem: Gem,
+  code: Code,
+  dumbbell: Dumbbell,
+  "gamepad-2": Gamepad2,
+  "graduation-cap": GraduationCap,
+  plane: Plane,
+  receipt: Receipt,
+  shapes: Shapes,
+  shirt: Shirt,
+  smartphone: Smartphone,
+  sofa: Sofa,
+  sparkles: Sparkles,
+  truck: Truck,
+  // lucide-react dropped brand/trademarked glyphs (no "Youtube" icon) — a
+  // generic video-camera icon is the closest available stand-in.
+  youtube: Video,
+  "zap-off": ZapOff,
 };
 
 export function getCategoryIcon(icon: string | null | undefined): LucideIcon {
   if (!icon) return Wallet;
   return ICON_MAP[icon] ?? Wallet;
 }
+
+// The full set of icon keys a category can be assigned, for the icon picker
+// in the category form — kept in sync with ICON_MAP above.
+export const CATEGORY_ICON_OPTIONS = Object.keys(ICON_MAP);

frontend/src/lib/navigation.ts

@@ -9,6 +9,7 @@ import {
   PieChart,
   Repeat,
   Settings,
+  Tags,
   Target,
   TrendingUp,
   type LucideIcon,
@@ -29,6 +30,7 @@ export const NAV_ITEMS: NavItem[] = [
   { labelKey: "nav.roi", to: "/roi", icon: Calculator },
   { labelKey: "nav.transactions", to: "/transactions", icon: ArrowLeftRight },
   { labelKey: "nav.accounts", to: "/accounts", icon: Layers },
+  { labelKey: "nav.categories", to: "/categories", icon: Tags },
   { labelKey: "nav.cashFlow", to: "/cash-flow", icon: Activity },
   { labelKey: "nav.reports", to: "/reports", icon: PieChart },
   { labelKey: "nav.budget", to: "/budget", icon: Target },