feat(web): add property comparison page with side-by-side view

Build a complete property comparison feature at /compare:
- Zustand store with localStorage persistence for selected listings (2-5)
- Side-by-side comparison table (price, area, price/m², amenities, location, etc.)
- Summary statistics banner (price range, area range, price/m² range)
- "Add to Compare" button on property cards and detail pages
- Floating comparison bar for quick access when listings are selected
- Bilingual i18n support (Vietnamese + English)
- 18 unit tests for store logic and comparison stats computation
- Mobile-responsive layout with horizontal scroll on comparison table

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/messages/en.json

@@ -215,5 +215,46 @@
       "10to20b": "10 - 20 billion",
       "over20b": "Over 20 billion"
     }
+  },
+  "compare": {
+    "title": "Compare properties",
+    "subtitle": "Comparing {count} properties",
+    "emptyState": "Select at least 2 properties to compare. Go back to search to select.",
+    "goToSearch": "Go to search",
+    "addMore": "Add more",
+    "clearAll": "Clear all",
+    "compareNow": "Compare now",
+    "needMore": "Need more",
+    "selected": "{count}/{max} selected",
+    "removeItem": "Remove",
+    "addToCompare": "Compare",
+    "removeFromCompare": "Remove from compare",
+    "added": "Added",
+    "loadError": "Unable to load data. Please try again.",
+    "retry": "Retry",
+    "property": "Property",
+    "noImage": "No image",
+    "remove": "Remove",
+    "price": "Price",
+    "transactionType": "Transaction",
+    "sale": "Sale",
+    "rent": "Rent",
+    "propertyType": "Property type",
+    "area": "Area",
+    "pricePerM2": "Price/m²",
+    "bedrooms": "Bedrooms",
+    "bathrooms": "Bathrooms",
+    "rooms": "rooms",
+    "direction": "Direction",
+    "floors": "Floors",
+    "yearBuilt": "Year built",
+    "legalStatus": "Legal status",
+    "location": "Location",
+    "amenities": "Amenities",
+    "projectName": "Project",
+    "priceRange": "Price range",
+    "areaRange": "Area range",
+    "pricePerM2Range": "Price/m² range",
+    "average": "Average"
   }
 }