feat: add Prowlarr integration for manual release search

Add Prowlarr indexer integration (step 1: config + manual search).
Allows searching for comics/ebooks releases on Prowlarr indexers
directly from the series detail page, with download links and
per-volume search for missing books.

- Backend: new prowlarr module with search and test endpoints
- Migration: add prowlarr settings (url, api_key, categories)
- Settings UI: Prowlarr config card with test connection button
- ProwlarrSearchModal: auto-search on open, missing volumes shortcuts
- Fix series.readCount i18n plural parameter on series pages

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/backoffice/app/settings/SettingsPage.tsx

@@ -580,6 +580,9 @@ export default function SettingsPage({ initialSettings, initialCacheStats, initi
       {/* Status Mappings */}
       <StatusMappingsCard />
 
+      {/* Prowlarr */}
+      <ProwlarrCard handleUpdateSetting={handleUpdateSetting} />
+
       {/* Komga Sync */}
       <Card className="mb-6">
         <CardHeader>
@@ -1217,3 +1220,136 @@ function StatusMappingsCard() {
     </Card>
   );
 }
+
+// ---------------------------------------------------------------------------
+// Prowlarr sub-component
+// ---------------------------------------------------------------------------
+
+function ProwlarrCard({ handleUpdateSetting }: { handleUpdateSetting: (key: string, value: unknown) => Promise<void> }) {
+  const { t } = useTranslation();
+  const [prowlarrUrl, setProwlarrUrl] = useState("");
+  const [prowlarrApiKey, setProwlarrApiKey] = useState("");
+  const [prowlarrCategories, setProwlarrCategories] = useState("7030, 7020");
+  const [isTesting, setIsTesting] = useState(false);
+  const [testResult, setTestResult] = useState<{ success: boolean; message: string } | null>(null);
+
+  useEffect(() => {
+    fetch("/api/settings/prowlarr")
+      .then((r) => (r.ok ? r.json() : null))
+      .then((data) => {
+        if (data) {
+          if (data.url) setProwlarrUrl(data.url);
+          if (data.api_key) setProwlarrApiKey(data.api_key);
+          if (data.categories) setProwlarrCategories(data.categories.join(", "));
+        }
+      })
+      .catch(() => {});
+  }, []);
+
+  function saveProwlarr(url?: string, apiKey?: string, cats?: string) {
+    const categories = (cats ?? prowlarrCategories)
+      .split(",")
+      .map((s) => parseInt(s.trim()))
+      .filter((n) => !isNaN(n));
+    handleUpdateSetting("prowlarr", {
+      url: url ?? prowlarrUrl,
+      api_key: apiKey ?? prowlarrApiKey,
+      categories,
+    });
+  }
+
+  async function handleTestConnection() {
+    setIsTesting(true);
+    setTestResult(null);
+    try {
+      const resp = await fetch("/api/prowlarr/test");
+      const data = await resp.json();
+      if (data.error) {
+        setTestResult({ success: false, message: data.error });
+      } else {
+        setTestResult(data);
+      }
+    } catch {
+      setTestResult({ success: false, message: "Failed to connect" });
+    } finally {
+      setIsTesting(false);
+    }
+  }
+
+  return (
+    <Card className="mb-6">
+      <CardHeader>
+        <CardTitle className="flex items-center gap-2">
+          <Icon name="search" size="md" />
+          {t("settings.prowlarr")}
+        </CardTitle>
+        <CardDescription>{t("settings.prowlarrDesc")}</CardDescription>
+      </CardHeader>
+      <CardContent>
+        <div className="space-y-4">
+          <FormRow>
+            <FormField className="flex-1">
+              <label className="text-sm font-medium text-muted-foreground mb-1 block">{t("settings.prowlarrUrl")}</label>
+              <FormInput
+                type="url"
+                placeholder={t("settings.prowlarrUrlPlaceholder")}
+                value={prowlarrUrl}
+                onChange={(e) => setProwlarrUrl(e.target.value)}
+                onBlur={() => saveProwlarr()}
+              />
+            </FormField>
+          </FormRow>
+          <FormRow>
+            <FormField className="flex-1">
+              <label className="text-sm font-medium text-muted-foreground mb-1 block">{t("settings.prowlarrApiKey")}</label>
+              <FormInput
+                type="password"
+                placeholder={t("settings.prowlarrApiKeyPlaceholder")}
+                value={prowlarrApiKey}
+                onChange={(e) => setProwlarrApiKey(e.target.value)}
+                onBlur={() => saveProwlarr()}
+              />
+            </FormField>
+          </FormRow>
+          <FormRow>
+            <FormField className="flex-1">
+              <label className="text-sm font-medium text-muted-foreground mb-1 block">{t("settings.prowlarrCategories")}</label>
+              <FormInput
+                type="text"
+                placeholder="7030, 7020"
+                value={prowlarrCategories}
+                onChange={(e) => setProwlarrCategories(e.target.value)}
+                onBlur={() => saveProwlarr()}
+              />
+              <p className="text-xs text-muted-foreground mt-1">{t("settings.prowlarrCategoriesHelp")}</p>
+            </FormField>
+          </FormRow>
+
+          <div className="flex items-center gap-3">
+            <Button
+              onClick={handleTestConnection}
+              disabled={isTesting || !prowlarrUrl || !prowlarrApiKey}
+            >
+              {isTesting ? (
+                <>
+                  <Icon name="spinner" size="sm" className="animate-spin -ml-1 mr-2" />
+                  {t("settings.testing")}
+                </>
+              ) : (
+                <>
+                  <Icon name="refresh" size="sm" className="mr-2" />
+                  {t("settings.testConnection")}
+                </>
+              )}
+            </Button>
+            {testResult && (
+              <span className={`text-sm font-medium ${testResult.success ? "text-success" : "text-destructive"}`}>
+                {testResult.message}
+              </span>
+            )}
+          </div>
+        </div>
+      </CardContent>
+    </Card>
+  );
+}