fix: cache_ttl config validation; ticket_web_url via tojson in base.html

- app.py: wrap int(cache_ttl) in try/except so a misconfigured non-integer value falls back to 3600 instead of raising ValueError
- base.html: use Jinja2 tojson filter for ticket_web_url to ensure proper JS string escaping regardless of URL contents

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.py

@@ -543,7 +543,11 @@ def api_avatar():
     os.makedirs(cache_dir, exist_ok=True)
     cache_file = os.path.join(cache_dir, f'user_{safe_name}.jpg')
     sentinel    = os.path.join(cache_dir, f'user_{safe_name}.none')
-    cache_ttl   = int(ldap_cfg.get('cache_ttl', 3600))
+    try:
+        cache_ttl = int(ldap_cfg.get('cache_ttl', 3600))
+    except (ValueError, TypeError):
+        logger.warning('Invalid cache_ttl in ldap config; using default 3600')
+        cache_ttl = 3600
 
     now = time.time()