feat: revised category icons + unknown type detection

- Cleaned CATEGORY_MAP: removed dead entries (Furniture, GF Bev,
  Snack/bev, Snack/food), fixed duplicate 'Food' key, proper
  distinct icons for all 6 real categories
- Added categoryInfo() helper: 🥤/🍿/🍔/🔧/🔌/📦 for known cats,
  ❓ (red) for unmapped categories, 📦 for null
- Updated all render sites (list, map pins, map list, detail view,
  scan result, OCR result) to use categoryInfo()
- Added category icons to detail view and scan/OCR result headers
- Synced categories DB table: added Equipment/Appliances with icons,
  removed unused Unknown
- Updated seed data in both server.py and admin_server.py to match
  real asset categories
- Added category_health to /api/stats with unmapped category detection
- Added Category Health card to admin dashboard (shown only when
  unmapped categories exist)
- Updated CSS backgrounds for all real categories + .cat-unmapped

server.py

@@ -342,8 +342,9 @@ def _seed_if_empty(conn: sqlite3.Connection, table: str, columns: tuple, rows: l
 def _seed_data(conn: sqlite3.Connection):
     """Insert default seed data for lookup tables."""
     _seed_if_empty(conn, "categories", ("name", "icon"), [
-        ("Furniture", "🪑"), ("Appliances", "🔌"),
-        ("Utensils & Serveware", "🍽️"), ("Equipment", "⚙️"), ("Other", "📦"),
+        ("Bev", "🥤"), ("Snack", "🍿"),
+        ("Food", "🍔"), ("Equipment", "🔧"),
+        ("Appliances", "🔌"), ("Other", "📦"),
     ])
     _seed_if_empty(conn, "key_names", ("name",), [
         ("MK500",), ("Green Dot",), ("Red Key",), ("Blue Key",),