Replace Basic Auth with login page, add HTTP redirect and log viewer

- Session-based login page instead of HTTP Basic Auth
- /ca.crt download works without login for easy device access
- HTTP port (default 8080) redirects to HTTPS automatically
- Nginx access/error log viewer in WebUI
- API still supports Basic Auth for curl/scripts
- Logout button and log navigation in header

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/templates/index.html

@@ -199,6 +199,8 @@
         <h1>HTTPS Reverse Proxy</h1>
         <div style="display:flex;align-items:center;gap:15px;">
             <a href="/ca.crt" class="btn btn-sm btn-primary" style="text-decoration:none;">CA-Zertifikat herunterladen</a>
+            <a href="/logs" class="btn btn-sm" style="text-decoration:none;background:#0f3460;color:#e0e0e0;">Logs</a>
+            <a href="/logout" class="btn btn-sm" style="text-decoration:none;background:#e74c3c;color:white;">Abmelden</a>
             <span class="badge">Self-Signed SSL - 100 Jahre</span>
         </div>
     </div>