i18n: migrate from German-first to English-first default locale

Switch defaultLocale from "de" to "en" and make English the code-level
language throughout. All ~145 hardcoded German strings translated:

- API error messages (52 routes) now return English
- Zod validation messages in English
- Classification/analytics functions return English categories
- Notification type labels in English
- Component strings use i18n t() calls (heatmap, mood chart,
  medication form, intake history, password strength, insights card)
- ~50 new i18n keys in both de.json and en.json

Route migration:
- /stimmung → /mood, /zielwerte → /targets (new pages)
- 301 redirects in proxy.ts for legacy URLs
- Sidebar + bottom nav updated

Bump version to 1.0.1.

src/app/api/admin/data/route.ts

@@ -30,11 +30,11 @@ export const DELETE = apiHandler(async (request: NextRequest) => {
     const body = await request.json();
     confirm = typeof body?.confirm === "string" ? body.confirm : "";
   } catch {
-    return apiError("Ungültige Anfrage", 422);
+    return apiError("Invalid request", 422);
   }
 
   if (confirm !== "DELETE ALL") {
-    return apiError("Bestätigung fehlt", 422);
+    return apiError("Confirmation missing", 422);
   }
 
   const result = await prisma.$transaction(async (tx) => {

src/app/api/admin/monitoring/glitchtip-test/route.ts

@@ -12,10 +12,10 @@ export const POST = apiHandler(async () => {
 
   const settings = await getGlitchtipSettings();
   if (!settings.glitchtipEnabled) {
-    return apiError("Glitchtip ist deaktiviert", 422);
+    return apiError("Glitchtip is disabled", 422);
   }
   if (!settings.glitchtipDsn) {
-    return apiError("Glitchtip DSN fehlt", 422);
+    return apiError("Glitchtip DSN is missing", 422);
   }
 
   const delivery = await sendGlitchtipEvent({
@@ -32,13 +32,13 @@ export const POST = apiHandler(async () => {
   if (!delivery.ok) {
     getEvent()?.addWarning("Glitchtip test event rejected: " + delivery.method + " " + delivery.status + " " + delivery.details);
     return apiError(
-      `Glitchtip-Testevent wurde abgelehnt (HTTP ${delivery.status ?? 502})`,
+      `Glitchtip test event rejected (HTTP ${delivery.status ?? 502})`,
       502,
     );
   }
 
   return apiSuccess({
     sent: true,
-    message: "Glitchtip-Testevent wurde gesendet",
+    message: "Glitchtip test event sent",
   });
 });

src/app/api/admin/monitoring/umami-test/route.ts

@@ -51,18 +51,18 @@ export const POST = apiHandler(async (request: NextRequest) => {
 
   const settings = await getPublicMonitoringSettings();
   if (!settings.umamiEnabled) {
-    return apiError("Umami ist deaktiviert", 422);
+    return apiError("Umami is disabled", 422);
   }
   if (!settings.umamiScriptUrl || !settings.umamiWebsiteId) {
     return apiError(
-      "Umami Script-URL und Website-ID müssen konfiguriert sein",
+      "Umami script URL and website ID must be configured",
       422,
     );
   }
 
   const targetUrls = resolveUmamiSendUrls(settings.umamiScriptUrl);
   if (targetUrls.length === 0) {
-    return apiError("Umami Script-URL ist ungültig", 422);
+    return apiError("Umami script URL is invalid", 422);
   }
 
   const appUrl = resolveAppUrl(request);
@@ -100,7 +100,7 @@ export const POST = apiHandler(async (request: NextRequest) => {
     if (upstream.ok) {
       return apiSuccess({
         sent: true,
-        message: "Umami-Testevent wurde gesendet",
+        message: "Umami test event sent",
       });
     }
 
@@ -117,7 +117,7 @@ export const POST = apiHandler(async (request: NextRequest) => {
 
   getEvent()?.addWarning("Umami test event rejected: " + lastStatus);
   return apiError(
-    `Umami-Testevent wurde abgelehnt (HTTP ${lastStatus})`,
+    `Umami test event rejected (HTTP ${lastStatus})`,
     502,
   );
 });

src/app/api/admin/notifications/test/route.ts

@@ -79,7 +79,7 @@ export const POST = apiHandler(async () => {
   if (channels.length === 0) {
     return apiSuccess({
       sent: false,
-      message: "Keine aktivierten Benachrichtigungskanäle gefunden",
+      message: "No enabled notification channels found",
       results: [],
     });
   }
@@ -89,7 +89,7 @@ export const POST = apiHandler(async () => {
     userId: user.id,
     title: "Test-Notification",
     message:
-      "<b>HealthLog Test:</b> Wenn du diese Nachricht siehst, funktionieren deine Benachrichtigungen!",
+      "<b>HealthLog Test:</b> If you see this message, your notifications are working!",
   };
 
   const results: Array<{
@@ -104,7 +104,7 @@ export const POST = apiHandler(async () => {
       results.push({
         channel: channel.type,
         success: false,
-        error: "SYSTEM_ALERT deaktiviert in Einstellungen",
+        error: "SYSTEM_ALERT disabled in settings",
       });
       continue;
     }
@@ -124,7 +124,7 @@ export const POST = apiHandler(async () => {
             results.push({
               channel: "TELEGRAM",
               success: false,
-              error: `Telegram API hat Fehler gemeldet (chatId: ${config.chatId})`,
+              error: `Telegram API reported error (chatId: ${config.chatId})`,
             });
             continue;
           }
@@ -139,7 +139,7 @@ export const POST = apiHandler(async () => {
             results.push({
               channel: "NTFY",
               success: false,
-              error: `Senden fehlgeschlagen (topic: ${config.topic})`,
+              error: `Send failed (topic: ${config.topic})`,
             });
             continue;
           }
@@ -153,7 +153,7 @@ export const POST = apiHandler(async () => {
           results.push({
             channel: type,
             success: false,
-            error: "Unbekannter Kanaltyp",
+            error: "Unknown channel type",
           });
           continue;
       }
@@ -163,7 +163,7 @@ export const POST = apiHandler(async () => {
       results.push({
         channel: channel.type,
         success: false,
-        error: err instanceof Error ? err.message : "Unbekannter Fehler",
+        error: err instanceof Error ? err.message : "Unknown error",
       });
     }
   }
@@ -173,11 +173,11 @@ export const POST = apiHandler(async () => {
 
   let message: string;
   if (failCount === 0) {
-    message = `Alle ${successCount} Kanäle erfolgreich`;
+    message = `All ${successCount} channels successful`;
   } else if (successCount === 0) {
-    message = `Alle ${failCount} Kanäle fehlgeschlagen`;
+    message = `All ${failCount} channels failed`;
   } else {
-    message = `${successCount} erfolgreich, ${failCount} fehlgeschlagen`;
+    message = `${successCount} successful, ${failCount} failed`;
   }
 
   return apiSuccess({ sent: successCount > 0, message, results });

src/app/api/admin/settings/route.ts

@@ -180,7 +180,7 @@ export const PUT = apiHandler(async (request: NextRequest) => {
   }
 
   if (Object.keys(updates).length === 0) {
-    return apiError("Keine gültigen Felder", 422);
+    return apiError("No valid fields", 422);
   }
 
   const settings = await prisma.appSettings.upsert({

src/app/api/admin/users/[id]/reset-password/route.ts

@@ -32,16 +32,16 @@ export const POST = apiHandler(async (
   const { password } = body as { password?: string };
 
   if (!password || typeof password !== "string") {
-    return apiError("Passwort erforderlich", 422);
+    return apiError("Password required", 422);
   }
 
   const target = await prisma.user.findUnique({ where: { id } });
-  if (!target) return apiError("Benutzer nicht gefunden", 404);
+  if (!target) return apiError("User not found", 404);
 
   const strength = checkPasswordStrength(password, [target.username]);
   if (!strength.isAcceptable) {
     return apiError(
-      strength.feedback[0] || "Passwort zu schwach (Score < 3)",
+      strength.feedback[0] || "Password too weak (score < 3)",
       422,
     );
   }

src/app/api/admin/users/[id]/route.ts

@@ -30,13 +30,13 @@ export const PUT = apiHandler(async (
   }
 
   const target = await prisma.user.findUnique({ where: { id } });
-  if (!target) return apiError("Benutzer nicht gefunden", 404);
+  if (!target) return apiError("User not found", 404);
 
   // Prevent removing the last admin
   if (parsed.data.role === "USER" && target.role === "ADMIN") {
     const adminCount = await prisma.user.count({ where: { role: "ADMIN" } });
     if (adminCount <= 1) {
-      return apiError("Der letzte Admin kann nicht degradiert werden", 400);
+      return apiError("The last admin cannot be demoted", 400);
     }
   }