feat: fix backend SQL columns, add dark/light theme, fix legacy CSS

- Fix 7 backend controllers: rename columns to match actual DB schema
  (name_room→room_number, id_room→id, bed_type→room_type,
   id_employee→id, status_employee→status)
- Fix 10 frontend files with matching property renames
- Add ThemeContext with dark/light toggle (localStorage persisted)
- Redesign theme.css with [data-theme] attribute selectors
- Add Google Fonts (Syne, DM Sans, JetBrains Mono)
- Redesign sidebar, topbar, and login page CSS
- Migrate ~44 legacy CSS files from hardcoded colors to CSS variables
- Remove Dashboards/Tableros section from menu
- Clean up commented-out CSS blocks across codebase

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

frontend/Frontend-Hotel/src/pages/RoomDashboard/components/RoomGrid.jsx

@@ -34,11 +34,11 @@ export default function RoomGrid({ rooms, onRoomClick }) {
           <div className="grid-5">
             {roomsByFloor[floor].map((room) => (
               <div
-                key={room.id_room}
+                key={room.id}
                 className={`room-card ${room.status || "available"}`}
                 onClick={() => onRoomClick(room)}
               >
-                <div className="room-number">{room.name_room}</div>
+                <div className="room-number">{room.room_number}</div>
                 {room.guest_name && (
                   <div className="room-info">{room.guest_name}</div>
                 )}