Add password visibility toggle to login; auto-sync admin password from ENV

- Login.tsx: Eye/EyeOff toggle button on password field
- main.py: _seed_admin() now updates stored bcrypt hash when ENV password changed

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

frontend/src/pages/Login.tsx

@@ -1,11 +1,12 @@
 import React, { useState } from 'react'
 import { useNavigate } from 'react-router-dom'
-import { BookOpen, Loader2 } from 'lucide-react'
+import { BookOpen, Loader2, Eye, EyeOff } from 'lucide-react'
 import { useAuthStore } from '../store/authStore'
 
 export default function Login() {
   const [username, setUsername] = useState('')
   const [password, setPassword] = useState('')
+  const [showPwd, setShowPwd] = useState(false)
   const [error, setError] = useState('')
   const { login, loading } = useAuthStore()
   const navigate = useNavigate()
@@ -43,13 +44,23 @@ export default function Login() {
           </div>
           <div>
             <label className="block text-sm text-gray-400 mb-1">Passwort</label>
-            <input
-              type="password"
-              value={password}
-              onChange={(e) => setPassword(e.target.value)}
-              className="w-full bg-white/5 border border-white/10 rounded-lg px-3 py-2 text-white placeholder-gray-500 focus:outline-none focus:ring-1 focus:ring-primary"
-              placeholder="••••••••"
-            />
+            <div className="relative">
+              <input
+                type={showPwd ? 'text' : 'password'}
+                value={password}
+                onChange={(e) => setPassword(e.target.value)}
+                className="w-full bg-white/5 border border-white/10 rounded-lg px-3 py-2 pr-10 text-white placeholder-gray-500 focus:outline-none focus:ring-1 focus:ring-primary"
+                placeholder="••••••••"
+              />
+              <button
+                type="button"
+                onClick={() => setShowPwd(!showPwd)}
+                className="absolute right-3 top-1/2 -translate-y-1/2 text-gray-400 hover:text-white"
+                tabIndex={-1}
+              >
+                {showPwd ? <EyeOff size={16} /> : <Eye size={16} />}
+              </button>
+            </div>
           </div>
           {error && <p className="text-red-400 text-sm">{error}</p>}
           <button