feat(i18n): full app + docs localization (de/en)

- translate remaining pages/components (admin, analytics, redundancy,
  trash, compare, browse, watchlist, admin tools tab, category combobox,
  theme toggle, tool preview card, tool-new/edit) to t() calls
- locales: 453 keys each, parity verified
- docs: bilingual handbook + release notes via *.en.md variants,
  language-aware docs.tsx (markdown paths, nav titles, search index),
  LanguageSwitcher in docs header
- generate-docs: emit per-locale handbook/release/search output,
  localized index.json fields (fileEn/titleEn), en-aware snapshots

artifacts/toolrate/src/components/category-combobox.tsx

@@ -1,4 +1,5 @@
 import { useState, useEffect } from "react";
+import { useTranslation } from "react-i18next";
 import { Check, ChevronsUpDown } from "lucide-react";
 import { cn } from "@/lib/utils";
 import { Button } from "@/components/ui/button";
@@ -23,7 +24,8 @@ interface CategoryComboboxProps {
   placeholder?: string;
 }
 
-export function CategoryCombobox({ value, onChange, placeholder = "Select or type a category..." }: CategoryComboboxProps) {
+export function CategoryCombobox({ value, onChange, placeholder }: CategoryComboboxProps) {
+  const { t } = useTranslation();
   const [open, setOpen] = useState(false);
   const [inputValue, setInputValue] = useState(value);
 
@@ -49,6 +51,8 @@ export function CategoryCombobox({ value, onChange, placeholder = "Select or typ
     (c) => c.toLowerCase() === inputValue.toLowerCase()
   );
 
+  const resolvedPlaceholder = placeholder ?? t("category.placeholder");
+
   function select(val: string) {
     onChange(val);
     setInputValue(val);
@@ -66,7 +70,7 @@ export function CategoryCombobox({ value, onChange, placeholder = "Select or typ
           data-testid="button-category-combobox"
         >
           <span className={cn(!value && "text-muted-foreground")}>
-            {value || placeholder}
+            {value || resolvedPlaceholder}
           </span>
           <ChevronsUpDown className="ml-2 h-4 w-4 shrink-0 opacity-50" />
         </Button>
@@ -74,7 +78,7 @@ export function CategoryCombobox({ value, onChange, placeholder = "Select or typ
       <PopoverContent className="w-full p-0" align="start">
         <Command shouldFilter={false}>
           <CommandInput
-            placeholder="Search or enter new category..."
+            placeholder={t("category.searchPlaceholder")}
             value={inputValue}
             onValueChange={(v) => {
               setInputValue(v);
@@ -84,10 +88,10 @@ export function CategoryCombobox({ value, onChange, placeholder = "Select or typ
           />
           <CommandList>
             {filtered.length === 0 && !showCreateOption && (
-              <CommandEmpty>No categories found.</CommandEmpty>
+              <CommandEmpty>{t("category.noCategories")}</CommandEmpty>
             )}
             {filtered.length > 0 && (
-              <CommandGroup heading="Known categories">
+              <CommandGroup heading={t("category.knownCategories")}>
                 {filtered.map((cat) => (
                   <CommandItem
                     key={cat}
@@ -104,13 +108,13 @@ export function CategoryCombobox({ value, onChange, placeholder = "Select or typ
               </CommandGroup>
             )}
             {showCreateOption && (
-              <CommandGroup heading="Create new">
+              <CommandGroup heading={t("category.createNew")}>
                 <CommandItem
                   value={inputValue}
                   onSelect={() => select(inputValue.trim())}
                   data-testid="item-category-create-new"
                 >
-                  <span className="text-primary font-medium">+ Create</span>
+                  <span className="text-primary font-medium">{t("category.create")}</span>
                   <span className="ml-2 text-muted-foreground">&ldquo;{inputValue.trim()}&rdquo;</span>
                 </CommandItem>
               </CommandGroup>