Add custom filter for DWS and Tanishq Dubey trademarks

- Create custom_filter.go with DWS/Tanishq Dubey term detection
- Block variations including:
  - DWS, Dubey Web Services, DWS Engineering LLC
  - Tanishq Dubey, tdubey
  - Leet speak variations (dub3y, t4nishq, dw5, etc.)
  - Combined terms (dubeydns, dws-ddns, etc.)
- Update frontend to show 'reserved' message for blocked terms
- Filters are case-insensitive and handle separators

Protects brand identity and personal name from being used
in user subdomains

internal/handlers/handlers.go

@@ -16,7 +16,10 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
-var profanityDetector = goaway.NewProfanityDetector()
+var (
+	profanityDetector = goaway.NewProfanityDetector()
+	customFilter      = NewCustomFilter()
+)
 
 type WebHandler struct {
 	db     *database.DB
@@ -57,6 +60,11 @@ func (h *WebHandler) ClaimSpace(c *gin.Context) {
 		return
 	}
 
+	if customFilter.IsBlocked(subdomain) {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "Subdomain is reserved"})
+		return
+	}
+
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
 
@@ -103,6 +111,15 @@ func (h *WebHandler) CheckSubdomain(c *gin.Context) {
 		return
 	}
 
+	if customFilter.IsBlocked(subdomain) {
+		c.JSON(http.StatusOK, gin.H{
+			"available": false,
+			"subdomain": subdomain,
+			"reason":    "reserved",
+		})
+		return
+	}
+
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()