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/Hotel/PropertyDetailPage.css

@@ -6,9 +6,9 @@
 .property-info-box {
   display: flex;
   justify-content: space-between;
-  background-color: #f8f8f8;
+  background-color: var(--bg-elevated);
   padding: 20px;
-  border-radius: 10px;
+  border-radius: var(--radius-md);
   margin-bottom: 30px;
 }
 
@@ -24,17 +24,19 @@
 input, select {
   padding: 5px;
   margin-left: 10px;
-  border: 1px solid #ccc;
-  border-radius: 4px;
+  border: 1px solid var(--border-color);
+  border-radius: var(--radius-sm);
+  background-color: var(--bg-elevated);
+  color: var(--text-primary);
 }
 
 .save-button {
-  background-color: #f2c300;
+  background-color: var(--accent-gold);
   border: none;
   padding: 10px 20px;
   border-radius: 20px;
   font-weight: bold;
-  color: white;
+  color: #000;
   cursor: pointer;
 }