Add German legal information and an impressum page for compliance

Adds an Impressum page, updates contact information on Privacy Policy and Terms of Service, and links to the Impressum page in the footer. Also updates the root HTML language attribute to German.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 2cd2c0bc-434c-4bc9-ad3f-b99d3897a0d1
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/8cc42625-c1f5-4e43-99bd-77f2c4dedee2/2cd2c0bc-434c-4bc9-ad3f-b99d3897a0d1/gjpMN2A

client/src/App.tsx

@@ -11,6 +11,7 @@ import GipfelstammtischPage from "@/pages/GipfelstammtischPage";
 import AdminPage from "@/pages/admin";
 import PrivacyPolicy from "@/pages/PrivacyPolicy";
 import TermsOfService from "@/pages/TermsOfService";
+import Impressum from "@/pages/Impressum";
 import NotFound from "@/pages/not-found";
 
 function Router() {
@@ -24,6 +25,7 @@ function Router() {
       <Route path="/admin" component={AdminPage} />
       <Route path="/privacy" component={PrivacyPolicy} />
       <Route path="/terms" component={TermsOfService} />
+      <Route path="/impressum" component={Impressum} />
       <Route component={NotFound} />
     </Switch>
   );