Add profanity filter for subdomain validation

- Integrate github.com/TwiN/go-away for content filtering
- Check subdomains for inappropriate content during validation
- Update frontend to display 'inappropriate content' message
- Blocks profane subdomains from being claimed

Uses go-away's built-in profanity dictionary to detect:
- Leet speak substitutions (e.g., @73447h013)
- Obfuscated profanity
- Common inappropriate terms

web/static/js/app.js

@@ -33,6 +33,10 @@ document.addEventListener('DOMContentLoaded', function() {
                 availabilityStatus.textContent = '✓ Available';
                 availabilityStatus.className = 'status available';
                 claimBtn.disabled = false;
+            } else if (data.reason === 'inappropriate') {
+                availabilityStatus.textContent = '✗ Contains inappropriate content';
+                availabilityStatus.className = 'status taken';
+                claimBtn.disabled = true;
             } else {
                 availabilityStatus.textContent = '✗ Already taken';
                 availabilityStatus.className = 'status taken';