Add password visibility toggle to login form

- Implement show/hide password functionality with eye icon toggle button
- Add dynamic input type switching between password and text
- Position toggle button inside password input field with proper styling
- Include hover, focus states and accessibility features (tabindex, title)
- Use FontAwesome eye/eye-slash icons for visual feedback
- Maintain secure default (password hidden) with optional visibility
- Integrate proper tab order with existing form elements

🤖 Generated with [Claude Code](https://claude.ai/code)

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

frontend/styles.css

@@ -534,6 +534,41 @@ body {
     font-weight: 400;
 }
 
+.password-input-container {
+    position: relative;
+    display: flex;
+    align-items: center;
+}
+
+.password-input-container input {
+    padding-right: 3rem !important;
+}
+
+.password-toggle-btn {
+    position: absolute;
+    right: 0.75rem;
+    background: transparent;
+    border: none;
+    color: #888;
+    cursor: pointer;
+    padding: 0.25rem;
+    font-size: 1rem;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    transition: color 0.2s ease;
+    z-index: 1;
+}
+
+.password-toggle-btn:hover {
+    color: #555;
+}
+
+.password-toggle-btn:focus {
+    outline: none;
+    color: #667eea;
+}
+
 .login-button, .register-button {
     width: 100%;
     padding: var(--control-padding);