feat: implement session timeout countdown and UI optimization

static/locales/en.json

@@ -8,7 +8,7 @@
     "nav_explorer": "Knowledge Explorer",
     "nav_calendar": "Calendar",
     "nav_nebula": "Knowledge Nebula",
-    "nav_logout": "Logout",
+    "nav_logout": "EXIT",
     "nav_settings": "Settings",
     "nav_toggle": "Toggle Sidebar",
     "nav_categories": "Categories",
@@ -35,6 +35,7 @@
     "settings_ai_enable": "Enable AI Features",
     "settings_category_enable": "Enable Category Feature (Advanced)",
     "settings_lang": "Language",
+    "settings_session_timeout": "Session Timeout (min, min 10m)",
     "settings_save": "Save Settings",
     "settings_reset": "Reset",
     "settings_close": "Close",
@@ -43,12 +44,14 @@
     "msg_delete_confirm": "Are you sure you want to delete this memo? This cannot be undone.",
     "msg_save_success": "Saved successfully!",
     "msg_settings_saved": "🎨 Settings have been saved to the server!",
+    "msg_session_timeout_min": "Session timeout must be at least 10 minutes.",
     "msg_ai_loading": "Gemini AI is analyzing the memo...",
     "msg_encrypted_locked": "🚫 Encryption detected. Decrypt first to modify.",
     "msg_auth_failed": "Invalid credentials. Please try again.",
     "msg_network_error": "Network instability or server error occurred.",
     "msg_confirm_discard": "Discard all current content and delete uploaded files from the server?",
     "msg_alert_password_required": "A password is required to encrypt this knowledge.",
+    "msg_session_expired": "⌛ Session expired. Please log in again for security.",
     "msg_draft_restore_confirm": "📝 There is an auto-saved draft.\nTitle: \"{title}\"\nWould you like to restore it?",
     
     "title_pin": "Pin to Top",